Turn the battery off and unscrew the cartridge or atomizer from your battery. Use a Q-tip or cotton swab dipped in isopropyl alcohol to clean the inside and around the rim of the heating chamber, and the bottom coil of your attachment. Also, make sure to clean the mouthpiece until all the residue is removed from the heating chamber.
Make sure to let the battery dry before using again. Be careful not to put too much pressure on the coil, as it is sensitive and can be damaged this way. Heating the chamber before cleaning can help loosen residue and make it easier to clean. Make sure both the battery and attachment are completely dry before screwing back together.