Hey Victor,
Improving your tuning on the trumpet isn't the easiest thing to do.
First off you have to know which pitches tend to be either sharp or flat on trumpet.
- low E on the staff is usually sharp
- low A and high A are usually sharp
- D on the staff tends to be flat
- low and high F tend to be sharp
- of course low D and C# are always sharp
These are a few, I'm no expert, but any serious legit trumpet player would have no problem explaining this stuff to you.