You will have a good chance at the practice fields in the early morning. You can also be one of the first in the ballpark and hang out near the dugouts. At Tempe Diablo, there is a spot down RF line where the players enter/leave the field from the clubhouse. You can catch them there.
Sosh HATES players signing during practice so if they don't stop to sign, that's a big reason why. Hamilton might make himself more accessible since he's on a new team. Pujols usually is pretty reserved but will sign at times. He won't sign jerseys, bats or on the sweet spot of a baseball. I've seen Trout sign frequently in the past, but not sure given his recent fame. A lot of the minor leaguers will sign freely. But whatever you do, respect their time. They do not have an obligation to sign anything.