This quote is from Doug Yeo, the former bass trombonist for the Boston Symphony Orchestra. My wife Tiffany is a band director in Fairfax County, Virginia and it came from her band room wall. This sums up practicing as well as anything can.
If you practice, you get better.
If you get better, you play with better players.
If you play with better players, you play better music.
If you play better music, you have more fun.
If you have fun, you want to practice more.
If you practice more, you get better...
That pretty much covers it, right?