how do you know what valve to pull if you are out of tune... i tune with my c

also, my left hand gets deadly tired after while of holding the trumpet up... any solutions to help me?

to answer your first question: you dont pull any valve. you pull the slide. the one that tunes all your notes is the biggest one, its the first one you find if you follow the lead pipe(where your mouth piece starts to where it curves) your regular spit valve will be on this slide. the third valve slide (the slide that comes from the third valve) is pulled out for some notes that arent in tune with the other instruments. for instance, you pull it out everytime you want to play a low C# or a low D. the spit valve on this slide is there because when you use your third valve slide spit collects in the slide. to release the spit push down the third valve slide, extend the slide out, and blow.
to answer yur second question: do push-ups, they help build your shoulders. just be glad your not in school varsity marching band... you HAVE to play with the trumpet above level while playing the music and marching around the field. hope that helps. p.s. were you the one who IMed me?

no, i didnt im you but if u want u can im me at HeadChefPalm. -thats my sn

If you are flat (lower than the note you should be) then you should push the slide in. If you are sharp (higher than the note you should be) then you pull it out a little.

Hope this helps,
Amy