Vasarely and other art prints  

As with any area of collecting, it helps to know your shit. It helps a lot. If you're decorating a dorm room, reproduction prints are fine. Otherwise, stick with original art. Specifically, art that you respond to and can imagine living with for a decade or more. If you're just starting out, visit galleries and talk to dealers that feature the kinds of art that you like. Try to buy from reputable dealers rather than online unless it's an established auction house. Anyone that's serious will offer guarantees. Beware of anyplace that won't sell a work on paper unframed or puts undue emphasis on frames. Don't be intimidated by prices or lack thereof. Be upfront about your budget and what you like. You'd be surprised at how many galleries' bread-and-butter business is in accessibly-priced works and how much you can learn from dealers that are in it for the long haul.
And watch it with Vasarely. There are fakes out there.

Persistence produces opportunities, and production value is very often extremely overrated
a symbol of the thing is often a reasonable equivalent to the thing, depending on level of saturation/immersion/addiction
a satisfying entry level can be as simple as a photocopy

having some semblance of rational motivation is vital
collecting for collecting's sake, or as "investment" alone... tends to suck hard pretty quick, I think
*raison d'etre*

Thanks guys, all good info.

For paintings - a quick touch of the surface, if possible, can tell you if you have a painting or a print. But beware there are textured prints out there as well so make sure the brushstrokes correspond to the texture.
For prints - look for plate marks where the paper laid on a plate and actually went through a press. Not all prints are made this way, but some of the better are. For non-pressed prints, make sure its hand signed and not signed "in the plate".