Commonly Used Spells
There are a few spells you use frequently in your hunt for crests. These include Incendio, Repairo, Depulso and Wingardium Leviosa. Some crests only require one spell, such as Incendio for burning away a plant that is in the way. Others require multiple spells to completely free the crest for you to pick up. Try different spell combinations in order to pick them up.
Minicrests
Of the game's 150 crests, 25 are acquired through the acquisition of minicrests. These fragments are picked up by destroying glowing objects with Depulso. By collecting 1,000 minicrests, you can acquire a single full crest. This means you have to accumulate no less than 25,000 minicrests during the course of the game, but it is also the only way to obtain these 25 crests.
Lion Statue Crests
There are 10 crests throughout the game that are held by lion statues. These statues require you to complete a side-quest in order to release their crest. Typically, these tasks involve dueling with other students or preparing potions. Each statue informs you of your required task, and releases the crest once you have completed it and returned to the statue.
Banner Crests
As you move through Hogwarts, you may notice several sets of purple banners hanging from the ceiling. Not all of these banners contain a crest, but at least four sets do. You have to completely unfurl the rolled up banners in order to see the crests.
Embedded Crests
Several crests are embedded in walls and must be dislodged by throwing an item at them with Wingardium Leviosa. You can distinguish these crests by the sparks they emit.
Crests Behind Gates
Some crests are located behind gates and are too big to slip through the bars with Wingardium Leviosa. In order to obtain these, you have to smash them against a wall and break them to pieces, then use Wingardium Leviosa to float the pieces through the gate, and Repairo to fix them.
Loose Crests
Many crests are simply lying around, waiting to be discovered. If you're thorough in your explorations of Hogwarts, you should find them all. Some of them will be broken, requiring you to use Repairo to fix them before they can be collected.