[Objective]

Not a graffiti artist, that creative outlet died out with the fines and my horrible drawing skills.

However:
Use cardboard or something a bit more solid than paper. I've seen too many people fuck this up for some reason.
It's better to use less paint than too much, dripping sucks and will most likely ruin the image of whatever you're trying to paint if you use too much. Might want to practice a bit beforehand to get a feel for the right amount, shouldn't take more than a couple tries to get a grasp of it.
If you plan to do this a lot: use a mask and gloves, those fumes are toxic as shit and have fucked people up for the rest of their life. If it stays on your hands for some time it'll seep into your skin and eventually your blood/system. I mean, nothing to care about if it's just tonight but ye. Serious health hazards if you're gonna do it a lot.