getting good takes practice that ull never put into a game (ie. the topic), so heres the short version.
strategy games, watch demos, copy build schedules (order and placement in which structurs are built to get the best startup for ur strat) and strats (strat eg. = drop 2 lurkers next to an enemy resource base -starcraft), strat doesnt have to be technical, but just an idea of what must be done, so u can replicate it.
FPS, watch demos, learn about angles (places to stand and shoot that result in the most effective defence or offence), learn about timing (ways in which u can calculate where an enemy might be or what he may be doing by the amount of time passed, this goes for items as well)
FPS tip works for cs and quake
anyway this is the short dodgy way that'll get u better than most noobs even if u have a bad aim, but thats pretty much it, u aint gonna get much further if the person ure playing has 1% more experiance. gl hf anyway