Memorize the position of the valves on your trumpet. The valve farthest from the bell is the first valve, the second valve is in the middle and the third valve is closest to the trumpet bell.
Play through the first few notes of a chromatic scale, starting on the note C. Play C by keeping all of the valves up and play the remaining notes by depressing the correct valves. Play C-sharp by depressing valves one, two and three. D will be played with valves one and three. D-sharp uses valves two and three. E uses valves one and two. F uses just the first valve and F-sharp uses the second valve. These are the only valve combinations you need to play the trumpet effectively.
Practice playing major and minor scales using a fingering chart to improve your understanding of the correct fingerings for each note. Practice the scales with the fingerings until you have correlated each note with a specific fingering. Memorize the scales so you don't have to refer to the music and fingering chart.