A big thing is the boat manufactures have no provisions to tie the wiring down.
While this kit may seem expensive....It works very well.
http://www.weldmountsystem.com/applications-marine.php
Don't even think about using the mounts with the double sided tape. They will last just long enough to get the boat out the driveway.
This is the type work I do and I'm anal about it. A clean wiring system will save you and impress your friends.....If they know what they are looking at?
All bends should be 90degs when laying stuff out.
You start at the Heart ...... The Battery/ Batteries...... I have certain battery trays that I use... I hate those stupid plastic straps that still let your batteries slide. This is a Attwood battery tray. When you loosen the tie downs they are removed to get them out of the way....Unlike some....This may make all the differance in the world where batteries are stuck in boats.
I install BEP battery Cluster switches..... This one is for a single engine and dual batteries
http://www.bepmarine.com/en/716-sq-140a-dvsr
It's superior to the Blue Seas -Add a battery, because it takes up less room and is so much more easier to understand which battery your actually connecting.....It has built in jumper cables and does things that take the worry out of battery management .
Wiring a boat correctly is not inexpensive....Using top grade materials..
I could write a whole book here....But I'm not going to.
The #1 main thing I see that is bad.......
Factory rigged boats have it, dealer rigged boats have it and people do it because they are cheap or ignorant.
It's the use of bare copper battery cable ends....... Don't use them.....They corrode! Use the tinned copper ends.
Your going to need the proper tool to crimp them...... Don't even think about doing it with a vise.