In a nutshell, fill with vodka and blow out a couple times until it's clear, then do the same with very hot water. Shake it with a thermometer type of shake a few times to remove most of the water. To empty it out even faster, search on "taryn spin" in ECF and make a spinner. Drying methods vary, and dense filler will take a day or two. My quick way is to set it battery end down on top of a light bulb for 15-30 min.
A carto that's not completely dry won't perform well - tight draw and no vapor.
Sometimes overfilling and blowing it out will get the older juice out for the most part and help with draw. The center hole/tube may be constricted. If you can't see light through it, try using a thin paper clip or needle, carefully pushing up from the battery end, to open it.
If your juice is thick, 50%vg or more or dark with sediment, cleaning will buy you time but not much. Thin clear juices give me the most life. Good luck getting more time out of it!