I usually just disassemble and rinse under somewhat hot water (don't wanna boil my fingers), until I can't smell the scent of the old flavor anymore. Then dry all the parts off, give the coil a dry burn, until it glows red and looks clean, then reassemble and add the new liquid/flavor and let it sit for a good 10 minutes before giving it a
vape. In addition to just filling the
tank, I usually add a drop of liquid to the coil itself, to "kickstart" the wicking.
Some flavors are quite a pain to get out of the wicks, especially when the coil and wicks are a couple of weeks old, in that case I simply change the coil to a new one and keep the old one for when I want to switch back to the old flavor.