One vital tip: Dont rely on smashes for KO's. Snake is far more unorthodox than every other newcomer here and his KO's come from his standard move set, hell even his AAA combo has the ability to KO in the right conditions. Not saying the smashes have their perks; Fsmash is ungodly strong but the range is short and the lag is heavy, Usmash requires some nifty aim or luck (unless you Cromslide it), and the Dsmash is proximinal so you can trip it by accident or your opponent can trip it via projectiles.
Everyone else covered the other tips though, youtube some tourney vids of Psycho ****** killing everyone in sight, practice and work on timing.