Some tips.....
*Hit F3 and F4 soon as you log into the server..you need to do those 2 things.."Join"...and "Ready". Else you'll just be spectating and wondering how to play.
*Always keep your health up...keep snagging those health packs
*Always replentish your armor..keep an eye on it...snag every armor pack you see. When you snag it..it prevents someone else from getting it until it spawns again.
*Upgrade your weapon right away. As you notice..that peashooter you spawn with is quite useless unless you keep bumping into someone.
At least get the shotgun..it's great for up close blasting...combine a shotgun, up close combat, with good circle strafing techniques..and you can take out any rocket jockey.
Rail gun has good damage...needs some precision shooting
Grenade launcher is fun...toss one into someones face that you are running towards, or lob them up ahead of you if someone is chasing you...you'll run past it..hopefully with good timing it will blow up as your pursuer gets to them. Or lob a bunch into a room that has a meelee of players in it.
Don't ignore those powerup goodies.
Leap off of the walls as you run...use those wall surfaces.