Assemble the components you will be using; engine, D/F finder, radio(s), GPS, tabs, etc. Anything that will have controls, instuments, power requirements. Most, if not all, will have wiring diagrams or schmematics and these will show the connections that will need to be made. Figure out where the various items will be located and what the lengths of the runs will be and add 15% min. to the lengths to the switches, instrument panels, power take offs, etc. Check out the link I will include because, aside from the soldering, shrink wrapping and terminal techniques discussed, it will also give you a chart of the industry (marine/AYBA color coding for wiring-very important and helpful. Make a copy of it and keep it on board!!! Helps with trouble shooting later.)
Get yourself a copy of Nigel Calder's "Boat Owner's Mechanical and Electrical Manual" and read it in sections. It will get a lot deeper than you will want to , but all the information is there and then some. It isn't cheap, (ask for it as B'day present, early Christmas present, be a "good" husband surprise gift, etc.) just get it!! It will save you much more than the price over time and will be a great resource for you and your friends.
Between the manuals and Nigel's book you should be good to go. One thought I have used is to run a heavy hot lead and ground to the helm/instrument panel and put each on a its own distribution post. From ther it save a lot of mutiple long runs. You will also likey want to keep ALL leads to units with any motors separate from your electronics (ignition noise).
Good luck and be well. Don't be cheap about it. Marine grade wire is more expensive, but it is tinned its entire length and as a result will last FAR longer in the marine/wet envirement other wire (Radio Shack, etc.) was not made for. Think of all the times you will be way out in 5'+ seas trying to get back in without a wire failure to deal with!!! Can you say Cheap insurance.
Oh yeah, get yourself a decent VOM meter. It is a life saver when you need to trouble shoot a problem. I got a second inexpensive one about the size of a cell phone that I keep in my water tight/desicant included tool box wrapped in foam rubber with an elastic around it. It has saved my butt a couple of times- Alt/voltage regulator or trim tab pump issues or old non-tinned wire from before I learned my lesson and didn't get to change yet!!
Take care and good luck.
http://www.screamandfly.com/home/hul...4/wiring_1.htm