Before you even think about gluing up any wood, first you should make a deatiled drawing or we can say a bluprint of all details. The purpose of this is so you know what you are in for before you start building. There are many how to make a guitar books out there and all have drawings to follow. Remember pencil can be erased but a band sawed or routed piece of wood can't.
The first thing you need to do is get a large piece of paper, I use tracing paper because you can easily lay a new piece of paper over it and trace the details that you have done and then maybe modify the body a little. This is also great because once you make one drawing and someone else wants the same pickup configuration or tremolo you already have it and can easily trace it.
It's a good thing to have a finished guitar body around to check the details on for reference , but you can wing it without one but the chances of making a big mistake are increased.
What I use to make a drawing on paper is the following. The paper, a small scale ( as you may have noticed I use millimeters) A long ruler, the ones I have are 3 feet and 5 feet long. The main reason I don't have a really long metric rule is because I would have to carry it on plane from Japan because they don't make them here. Also I do all my scale length calculations in inchs because this is the standard. I keep templates around for humbuckers, tremolo routs and control cavities that I have made before to speed up the drawing process. If I need to make some new drawings I first do it on paper then make a template of it for next time. Other things that are important is a neck so you can get all the placement right and for a outline I use a flexable scale that can be shaped to multiple radius for the bodies shape. ( See computer drawing below) also I have a digital caliper and a set of radius gauges I bought in Korea these are hard to find here but you can make them if you really want them.
The most important part of the drawing is first the center line, without this everything will be off. Take the long ruler and make a center line down the paper all the other parts will be set to this. The next part is up to you but I found the best way unless I have a body to trace is to lay a neck on the paper at center and trace the area of the neck and body joint. To find the center of the neck just measure the width of the neck at the bottom and split it in two ,this is center.
If the drawing will be a set neck or neck through you will need to make a basic drawing of the neck first so you know where to put everything. What you need is the nut, twelth fret and the last fret. It really helps to have a slotted fretboard or a complete neck to lay down this is the most accurate way, if not you will need to figure it out mathmatically. (See scale calcultion chart)
After drawing the center line lay the neck on the drawing and mark the 12 fret and draw the neck pocket for the neck in the exact position with the 12 fret. After the neck pocket is in the drawing figure out the bridge position next and mark it, to do this take the total scale length and divide it by /2 then measure from the twelth fret to the body, we will compensate for intonation later. (a 25.5 inch scale is 12.75" from the twelth fret to the body scale location.
Next figure the pickup position, This is not hard but there are some different ways to do it. The "this looks cool way" where you put them so that it looks good, usually this is as close to neck as possible and fairly close to the bridge. Another way that I do it is to take another guitar with the same scale length and play the harmonics over the pickups and find the location of the strongest harmoinc points and mark it from the twelth fret then put lines on the drawing. ( if you will use mounting rings remember to ad enough room so that the rings clear the end of the neck and the tremolo when it is used.) Sound wise the closer a pickup is to the neck the more bass responce and the closer to the bridge the more treble responce. I will set the humbuckers on this guitar at center to the strongest harmonic location. Next flip over the pickups and draw the outline of the bobbins at center, If it is a single coil I trace the bottom of the pickup because of its shape.
Lets figure the complete heel or neck pocket area and draw it in I will use a neck plate for this guitar so I lay the neck plate on center in the neck pocket drawing and mark the four hole for the screws then trace the plate, from the plate drawing I ad 5 millimeters all around and draw it, this will be the final neck area.
Now take the bridge that will be installed and find the center of it by measuring the saddles to center. Move the bridge saddles so there is room to move the intonation forward and backward, set the High E string as a reference and move the low E string saddle back 5 mm's from the high E string this will give enough movement for the intonation. Lay the bridge on center to the drawing and from the scale line that we drew lay the high E saddle 1.5 mm's back and trace the bridge.
Now if the customer gave you a drawing, find the center of the drawing and make a line. If you are copying another guitar find the center and lay it on center with the neck pocket as a position guide and trace the body. Find the knob and switch locations marked from before and draw the location. Lay a knob at the point and trace it. Get up go to lunch or get some coffee because you will need to focus now.
Ok your mind is fresh look at the drawing and first figure out what does not make sence maybe the tremolo runs into the back of the guitar or the control's do not have room or the guitar does not look ballanced. Clean up the body outline by using a flexable ruler by finding two points around the body and bend the ruler until it looks like a good shape then draw the line. This can be a large section of the guitars outline and does not need to be just a small area. Keep doing this erasing things and adding things until the guitar 's shape is perfect and I really mean perfect there is no second chance. If it is a customers personal design ask them to come look at it and you can explain any changes and maybe do some modifications while they are there.
After this is finalized you will need to draw the routed areas on the paper for the pickups, tremolo and control cavity routs. My system is all routs on the front are regular lines and all routs on the back I use a dotted line. What ever the depth needed for the rout is, figure it out and write it on the drawing. Maybe the humbucker needs to be 25 mm 's deep but the screws for the humbucker need to be 32mm. Mark this and remember the less wood routed is probaly better. (Some people have a different oppinion on this). If the cavity plates are recessed draw this on there to. I usually measure away from the routs 7 mm's and then draw the outline of the plate. Then figure out where the screws will be and make sure there is enough room for the screw to go into the wood without breaking out the side. This is a mistake I made only once and it was a pain to fix I had to drill 12mm holes at the screw holes, epoxy dowels in and reshape them to hold the screws.
Thats it for drawing by hand if you want to start making a guitar you should make templates from the drawing, See Templates.
Moving The Design Into Production
After the prototypes are finished it is time to move the guitar into production. The factories will need detailed drawings to work from, this is so that there will not be any chance of mistakes during production.
What is done next is that we complete a final specification sheet. The spec sheets have all the information that you will need to start producing the guitars. The first page of this chapter has a standard form specification sheet that I use to finalize the designs. Spec Sheet Template.
After the specs are finished it is time to do the Cad drawing, Some programs like Bobcad Cam actually run the CNC after the drawing is made so this is convenient.
Many people I talk to use different drawing programs for there own specific reasons. I started and still prefer AutoCad for most design work because of its simple interface, I have tried Many Cad programs but the only one that is easier than Autocad for many operations is Bobcad,. I have not tried every program because they are so expensive but I still recommend from my experience one of these.
To start a Cad drawing we need to have a basic layout hand drawn, I use graph paper in millimeters, This is impossible to find in the states so I get it in Japan. From my book you can tell that I prefer metric.
Take the graph paper and start with a center line down the middle this will be 0 on the X axis, Then trace the body or neck layout on center. After the body or necks is traced onto the paper we use radius gauges all around the body to check each arcs location and radius. Mark the points of the beginning of the radius and the end of the radius as it follows the gauge.
Completely layout every radius on the drawing so that the drawing is now broken down into 
multiple radius.
Now we need to find the X and Y coordinates for each arcs location, to do this start at the center line anything to the left is Negative X any on the right side of the center line is Positive X. For the Y coordinates I start at the lowest point on the drawing say the lower bout and make that 0 on the Y axis.
Just to make it easier for me I write the numbers on the graphs at 5mm intervals so that I can easily see where I am on the page. Start at a flat area like the neck pocket and work your way around the drawing, measure the distance from the center Line in Y and X and make a note for example X=-39.3 Y=28.71 this is the start of the Arc, the Arc ends at X=-47.09 Y=40.38 The radius between the two is 30mm. This is one line in the program.
I usually do this type of drawing in Bobcad because it has a points menu that you can type in all the coordinates by points of the XY Axis and then after all the points are typed you can select two points and add the radius, this is really quick after you get all the X and Y locations.
You do the same with all the pickup or pickguard routs and enter all the information into the drawing, If you are working in 3D than you will also have a Z axis that is basically the depth of the routs. I start on a flat surface as 0 and anything below is Negative Z. If the pickup rout is a depth of 25mm this would be Z=-25.
Another interesting feature in the Bobcad program is the offset curves feature this will automatically offset and area by any number you want. If you are putting binding on the top and it will be 5mm thick than you can select the body outline, select offset curves, put in the distance of 5mm and it will put the binding channel on the drawing. I also use this for designing arch tops by using 10mm offsets and continuing the curves until it reaches the center, Bobcad automatically compensates for the differences to center. For the round over on the body I also use the offsets, if the round over is R12mm than I set the offset to 6mm.
Once the drawing is finished, we use it to either make the templates or to make the actual CNC program that will cut the bodies. The drawing will always be the main reference for all production models.