Rahul is correct, gamification isn't a system to apply, it's really another set of design strategies, with all the artistry, pondering, and tradeoffs that that implies.
However a currently popular set of game mechanics (that are powerful, but often incorrectly used) are points, levels, badges, trophies, and virtual currencies.
A great way to start is to ask "what game are my users already playing?"
Usually there is some emotional reason people already engage is this type of experience. Once you find that, figure out a simple, clear, visually appealing way to display their progress in achieving that emotional goal (perhaps points). Then show progress toward milestones (maybe with levels) and celebrate their completion with rewards (badges, trophies, power, access, etc.)
This is just the tip of the iceberg, but should get you started in the right direction.
(You should also study successful games or gamified experiences that are as similar to what you're working on as possible.)