NOOB question re: print quality.

Just starting out with a 450D + kit and I was wondering why some (not all!) of my shots look very detailed on the computer but often look average when printed? I usually just get my prints done at a local camera store - is there some trick to getting more detailed prints?

Google "sharpening photos". Other than that just use a decent lab like mpix, though most labs do a decent job these days, they use the same equipment and it's hard to stuff things up.