I would definitly suggest investing in master test kit that'll tell you ammonia, nitrites, and nitrates. If not, take some water to your LFS and tell us the results. Algae can come from a lot of things including overfeeding (too many nutrients in the tank), high nitrates (thus lack of water changes), and excessive lighting. Algae is normal in an aquarium; it's healthy for it to have some. Brown algae wipes off really easily if you get yourself an aquarium sponge.
Should you get...
Plants: Sure, why not. They munch up excessive nitrates and are nice to have. On the other hand, make sure you're getting ones that are easy to grow in low light (Java Fern, Wendtii, Anacharis...) so you don't have to get a stronger light or add CO2.
Pleco: Eh, up to you. Plecs, especially Commons, aren't really interested in algae once they discover there are other sources of food for them. I'd suggest finding a Bristlenose plec if you want an algae eater. Otos are a good choice too, but you'll need a decent school of them (make sure your water checks out before getting otos; they're a bit sensitive).
Snails: I've never found snails to be super effective when it came to algae munching.
Either way, it'd be really helpful to get your water checked out before you add anything.