PLEASE BE NOTED THAT EXPERIENCE LEVEL WILL NOT DEFINE YOU AS A "GOOD" PLAYER.
That being said, some clans may require you to be at certain level to gain in-clan memership. Other than that, levelling up fast will not earn you anything.
In Clash of Clans, the more experience you gain, the higher you can level up. And experience (also known as XP) can be gained by several ways.
UPGRADING YOUR BUILDINGS
Upgrading buildings is always the most effective way to level up in COC, especially collectors, mines and also defensive buildings, which can guard your town hall and resources. The more resources you save, the more buildings you can build, or the higher your buildings' level can be upgraded to.
RAIDING, COLLECTING, AND THEN UPGRADING
Other than collecting from mines, COC players can also collecting resources by raiding town halls. With those resources you've collected, you can upgrade your defensive buildings, which can protect you from being raided, and resource buildings, which will generate more resources for you. So raid more, collect more resources and upgrade buildings.
Achievements can gain you experiences as well as gems but it does take a lot of time to complete.
CLAN HOPPING - DONATING TROOPS
The whole "Join a clan - Donate all things possible - Leave and join another one" thing is called clan hopping. The experience you gain depending on how hign your troops are. So train high spacing troops like dragons and then join a clan, waiting for troop request, donate them and join another clan.