I think starting out, you really, really need to use your mouse/keyboard. I know there are those PantherXL people that love it...but mouse/key really will begin to feel natural.
First. Your keys should be mapped out to:
W - forward
S - backward
A - strafe left
D - strafe right
space - jump
Your mouse should be:
button 1 - primary fire
button 2 - secondary fire
My wheel selects weapons up and down. Pressing the wheel gets my best weapon.
People will argue over what keys should do what...but this is a good basic set-up.
The keys around your movement keys should be for the best weapons. ex:
Q - Flak Cannon
E - Rocket Launcher
Caps - Minigun
Shift - Shock Rifle
etc.......
If you are going to play team games you should master the translocator. My key to select it is the R key. Use it alot.
The first thing you should do is get comfortable with your setup. Start a practice session with no bots. Get used to moving around quickly. Get used to maneuvering through the levels backward (yes backward). As you run through a hallway, practice doing a 180 degree turn on the run.
Then learn your weapons - primary and secondary fire is a must to know. Read and learn the different ways to use them. Think of your mouse as your gun and your head all in one. practice turning and shooting.
Now Start a Tournament and play the tutorial maps. Beat the game on the easiest setting. Go back and increase the skill level each time until you reach at least Masterful.
By this time you should be ready to play online. I suggest you spectate a game or two (check spectator box in the options). Then hop in! You'll probably get trounced a few times...but you should be able to put up a fight at this point.
Read and learn what you can about the game, it's secrets, tips...anything. A good place to start is at Planet Unreal and look through the different sites. Cleaner runs a nice site with a virtual wealth of knowledge
here.
Have fun!