if your playing for the first time then i guess its woodsball?
Well, just stay in tight in your cover, communicating with other player goes a long way: If you want cover fire ask for it.
Urm...if theres an option to get a better marker (£5 or so) then go for that. It will be a real help, and uh, buy loads of paint
New pads etc will cost around 30 (JT skinz)
Guns go for anythin around £100-900, plus a decent hopper £45 new(X board revvy) to a Halo B for 90
Then you will need Co2 or Air-New Co2 for 45, 2nd hand for 20 or under
Air goes for £70-400 new but can be gotton on here for about 70-250ish