Watershed said:
Start in the middle, and work your way to the edges of the template.
I also covered the finished surface in blue painters tape as not to have any scratches.
I strongly agree with these two suggestions. I did the same to an unfinished body, but the blue tape prevented the wood shavings from getting trapped between the router base (template) and the body, which would have scratched the body a lot.
In my opinion, you should NOT MAKE YOUR FIRST ROUTE at the full depth of the pickup. It is best if you start with a very shallow route (say 1/8" deep) and then make successive passes at incrementally deeper settings. When I was young and had no sense (last year) I tried doing this on a scrap piece of wood, with the router bit set at approx 3/4" depth. This was a BAD IDEA because the router bit ended up grabbing the piece of wood and spinning it around before the bit had gone to its full cutting depth. That was a quick and painful lesson in how NOT to operate a router!
This is especially critical if you are working with a very dense/heavy body wood that can chip or splinter.
Combining this idea with the previous suggestion of working from the middle to the outside is probably wise. On each of the initial routes, try to stay back from the actual edge of the pickup cavity by 1-2mm, then on the last pass (at full depth) you can very carefully work your way to the outside and define the pickup edge.
Move the router slowly and cautiously, but don't leave the bit spinning in the same place for too long. Keep moving. Oily woods like Rosewood and Purpleheart will start to burn if you leave the bit in one place. That smells NICE. (not!)
Most experts who've routed will tell you that you need to move the router clockwise (or counter-clockwise) to work the cutting surface of bit AGAINST the direction of the cut. This should work better than the opposite, which allows the bit's cutting action to push the bit away from the wood. I'm not an expert, so you should probably do a bit of research on this.
If you're planning on a more complex route (such as a Jazz pickup) you should really get a template made up. For a bass bridge pickup, consider starting with a simpler shape such as an EMG soapbar until you get some hands-on experience.
Finally, the old adage about cutting wood applies here:
"Measure twice, cut once, swear like a sailor, then buy another." :icon_jokercolor:
