Leveling

Each Growtopian has levels, and you can gain levels by breaking blocks, farming, and earning Achievements. All of those activites will give you XP. The highest level you can reach is lvl 99. Once you hit certain level milestones, you earn certain achievements. Leveling up to level 10, for example, gives you the DING Achievement, and leveling up to level 50 will give you a Mini Growtopian. There are a lot of players who think that the higher level you have, the better you are. This is false, as levels are only really a measure of how much farming a player does. Seth and Hamumu may add some more features to do with leveling in the future.

As of the 03/01/2016, The way XP is earned has changed according to Hamumu, on the "Announcements" sub-forum

Collecting Gems does not give XP anymore. On the other hand, breaking blocks gives up to 20x more XP depending of the rarity. The XP earned per block is calculated by rarity/5. For example, a Crystal Block would give 20 XP when destroyed.

Trees gives twice more as XP as they used to give when harvested.

Also, most of the mini-games like The Carnival, Surgery, Sewing, Fishing, and Forging... They now give 1-100 XP.