The first bit of advice I have for you is to find out (if possible) what oil mix the previous owner of the bike used. The reason the exact mix is important is that changing the oil to gas ratio can change the carburetor jetting requirements, so if the bike had been previously set up for a certain mix it will run better if you stick to it. I also recommend using the same brand of oil, just to be on the safe side.
Next, if you haven't already, you need to get a decent helmet. Don't be a fool and ride without it, even just messing around in your back yard or empty field. You WILL fall. A good set of motorcycle boots, gloves, chest protector and knee pads will make the falls a lot less painful.
Other than that, start her up and ride! Come back when you have specific questions. Enjoy!
Rod