OK so now we have a short list of things we need to do before we can start diagnosing what's going on with this bike.
1. Drain out all the gas from the tank. Remove the tank, take off the petcock, and let it all drain out into a bucket. Take a note of what condition it is in. Fresh gas is just about clear, the older it gets the yellower it gets. Piss-colored gas is not very combustible, a bike won't typically run well on it, but it won't clog up your carbs either. Even older gas will get sticky and thick like varnish. Also look for flakes of rust coming out. A little bit is not such a big deal, I mean come on its an old bike, give it a break. But a lot might mean re-sealing the tank, removing the rust, or replacing the tank. Its up to you, but the presence of varnish or rust will almost guarantee that a carb cleaning is in your future. Recycle the old gas appropriately, its nasty stuff don't pour it down the drain.
2. Take out all the spark plugs, and drip a little bit of oil into each cylinder, about a teaspoon. Motor oil will do, or foaming oil, just something to lube up the cylinders. Especially if your bike has been sitting for quite a while, if you fire it right up it will take a bit for oil pressure to pump oil up to your cyls, and during that time damage is occurring to your rings, cylinder walls, etc. So pre-lube it and avoid that.
3. While your spark plugs are out, either clean them up with some fine-grit sandpaper, or replace them. Gap them appropriately.
4. Change the oil. Chances are your oil is disgusting, contaminated, or otherwise unsavory. No reason to pump all that junk all through your bike. So drain it out and toss in some fresh 10-40w, or whatever your bike calls for, fully knowing that once you get the bike running, you'll be doing another oil change before you put it back on the road. Seriously these oil passageways do get clogged up especially if you pump junk oil through your motor. So you can do all this work on a vintage bike and get it all going, and then clog your oil passageways and destroy the motor, or you can just toss in $10 worth of oil now and avoid that eventuality.
5. Pull out that old junk battery and recycle it. It would be a good idea to get a new battery, and many stores will take the old one in on a core refund and give you some money back. I know Walmart carries a lot of motorcycle batteries and will give you $9 back for your old battery. So you can replace it now if you want, or you can use jumper cables from a car battery to start/diagnose the bike for the time being, but regardless the old battery should be out. If you leave it in, it will just be a drain on the good battery, and might even cause a short.
6. Put the bike up on the center stand if it has one. If not, consider getting a rear wheel stand and put it up on that. Make sure the bike is in neutral.
7. With the tank and seat off, take a good hard look at all the components of the bike. Take a nice, slow walk around the bike and look at everything. You may or may not be familiar with all the components of the machine, but look for anything that looks out of place. Clear out that old mouse nest. Hook up that disconnected coolant hose. Click together that electrical connection. Don't worry about the fuel overflow hoses coming off the bottom of the airbox or the carbs, those are supposed to hang free. But pretty much everything else should be hooked back up. Do your best, you'll know what all this stuff does before too long.
8. Buy a repair manual! If you are at all serious about owning a vintage bike, you must have a repair manual made out of paper. "But Max!" You say. "I am too cheap/impatient!"