It depends on how old the bike is. Does it start now? If so, your job will be much easier.
Start with the brakes, see what color the fluid is. If its too brown to see thru, flush it out. Basically keep bleeding it, while filling up with new fluid from the master, untill you see clear fluid come out the caliper.
There is a good chance you will have to jump your bike. That does not mean that there is anything wrong, but it could mean that your battery is dead.
Engine oil tends to turn acidic if you leave it for a long time, and this could eat up your alternator. This will be expensive to fix, but it only tends to happen to older bikes. Either way, new oil and filter.
Look at the tires carefully, especially where they touched the ground. Chances are there will be some rot in those spots.
Syphon as much gas out of the tank as possible, fill with new gas, plus half a bottle of cleaner. If your bike starts, let it idle for a long, long time to flush the fuel system. If your bike is carbed, you may have bad gas in the bowls, so drain them (screw under each bowl) you may also have gunk blocking the jets, for which you will need to take the carbs apart.
Clean and oil the chain, and check if there are any linkages that need oil (axles, swing arm pivots, steering head etc) they are probably fine, but check.
Let us know how it goes. It could be a simple oil change and you are back in buisness, or it could be a ton of work on the electrical system.
Is there anything I'm forgetting?