1) Use lots of air all the time, regardless of what you are playing.
2) Don't put too much pressure on the mouthpiece, especially when playing higher notes.
3) If you're in a band, play what you see on the sheet music, not what you think it should sound like.
4) Practice every single day that you can, for at least 20 minutes per day.
5) Have fun! You will sound better at the trumpet if you enjoy playing it!
I hope these tips will be of use to you! If you have any questions, let me know!