One of the most common complaints about Glocks from shooters of other firearms is the trigger.  Most 1911 shooters hate the Glock triggers because of the striker-fire mechanism used.  By default most Glocks have a 5.5 pound trigger pull.  You have 2 popular choices to lighten up the trigger pull.

1. Trigger connector replacement
2. Challenger/Edge trigger kit

The trigger connector is the easier of the two and is also the cheapest.  A few companies produce these and it only takes about 10 minutes to install and brings the pull weight down to 3.5 pounds.