A few points that I don't think have been mentioned:
1. It is easier to pass the ball in the direction you are facing - don't assume you always have to go up the field - if you are facing towards your own goal and get the ball, see if there is someone behind you (or to your side) to pass it to
2. Don't assume your job is done once you have gotten rid of the ball to a team mate. His/her easiest pass is probably back to you. In any case, move away from the person who is marking you and give them the option of passing back to you.
3. Following on from 2 - support the person carrying the ball - and as already pointed out - call out loudly to let them know you are available. If you do 50 runs into space in a game but never get the ball, that is OK - everytime you move, the opposition defence has to reset, so you are making a gap for other team mates.
4. Don't be afraid to shoot - too often you see people f@$ing around with the ball inside the box, waiting for the perfect opportunity.
5. This may sound kinda simplistic, but control the ball before trying to do something with it. As you become more proficient, you can start doing one touch stuff, but when starting out you are better to stop the ball, then decide what to do with it. More speed less haste!
6. Lift your head up and look around. Hopefully you should be confident enough to run with the ball without looking at it too much...
7. Finally - I second the stay on your feet thing - slide tackles are last resort only - and you better hope they come off
