Agree totally with Makomark on wire and terminals.
I would start with the battery wiring. If you are using a dual battery setup. install a top quality four position battery switch that allows you to select individually battery 1 (typically for starting & running the motor), battery 2 (for all other equipment), both batteries for charging and battery backup, and OFF. Diagrams for that wiring setup are all over the Internet. If you are doing only a one battery setup wire in a single cut-off switch that's easy to access so that when that switch is in the "off" position, you are absolutely sure everything on the boat is off EXCEPT the bilge pump, which should be wired directly to the battery. Use top quality marine cables from the battery to the engine and make sure the connections are clean and tight. Do not use wing nuts for the connections to the battery terminals, but rather good quality SS lock nuts.
If you plan on installing a bilge pump, I would do that next. The bilge pump should be wired such that the float switch will turn it on independently of the manual switch. Again, diagrams for that set up are all over the internet.
Next, wire in the harness from the engine to your console key switch and instruments. Depending on what engine you have and its age, and the engine-dependent instruments you will be running, it may be worthwhile to purchase that harness from the engine manufacturer. Otherwise make your own. Use different color wiring for each engine circuit and document what color does what, and be consistent with your color codes. Replicate the NMEA wiring standards as close as possible to save future headaches. You can purchase roles of different colored marine wire from West Marine or Jamestown Distributors.
Finally, assess what other power draws you will need to wire up - running lights, VHF, fish finder, GPS, etc. For those, add up the total max draw in amps. Then from standard wiring charts, figure what gauge wire will be needed to handle all of that. For example, if you are pulling 20 amps, and your running the wiring ten feet from the battery, you should use 10 gauge (AWG) wire. Then, figure out how many fused switches you will need on the accessories bus, and install the bus in your console. Install two heavy duty connectors near the house battery - one for positive feed, and one for negative feed. From those run your 10 AWG (or whatever you calculated) to the accessories bus in your console area. It may be a good idea to install another cut off switch on the positive lead to the accessories bus. Then wire in each of your accessories.
