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 trim of the heating chamber as well as the bottom coil of your attachment. Also make sure to clean the mouthpiece until all the residue is removed from the heating chamber.
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.