Several things to do:
1. Buy a battery tender(a low current motorcycle battery charger, not the ones for car batteries as they will overcharge and ruin your battery).
2. Purchase a shop manual with the wiring diagram or ask BTK if they can get one for you or try
Repair Manual Catalog Online - RepairManual.com
3. Buy a small brass bristle brush and some 400-600 grit sandpaper to clean the electrical connections and some good electrical contact cleaner(not WD-40!) A good brand is De-oxit
www.de-oxit.com
4. Doing one electrical connection at a time(bullet connectors,square or rectangular) clean/remove the green crud of corrosion as this is non conductive.
5. The battery is a critical part of the electrical system on the motorcycle and should only be disconnected while performing a tests.
6. All battery terminals must be clean and tight, at the chassis ground/engine and at the starter solenoid terninals
7. The handle bar switches will probably require cleaning as the age of the bike might make them intermittant in operation.
Cleaning the electrical system is not to be rushed as it is the nervous system of the bike.
Keep us posted on your progress as others will suggest things to check or replace
I'm just covering the electrical basics and other people will touch on valve clearance,fuel delivery and tank condition,tires,control cables,brakelines etc.