If you are new to TO or any kind of mod like it, first, do not wander off on your own. Find a group of fellow team members and follow them around, perhaps you can cover the rear. Watch what they do and try and do what the more successfull players do.
Second, don't give up. It can take awhile to learn the limits of what you can do and the maps. Knowing the maps helps a lot.
Third, watch how the other team plays. If they rush or camp at their base, you'll have to learn to be flexible enough to adjust your play in accordance to how the other team plays.
Fourth, try and use the different weapons to get the feel for them and to decide which ones work best for you.