When their performance drops off is when I do it. That would be less vapor, burned taste or if you want to change to a completely different flavor you might want to clean it first. I use this method:
1. Blow out your atty until no more
juice comes out.
2. Over the sink, put some baking soda in the open end of the atty then add vingegar.
3. Quickly plug both ends with fingers so that the "eruption" comes out the air holes on the side.
4. Repeat until liquid coming out is clean looking.
5. Rinse atty under running water and blow out about 10 times. (Rinse/blow, rinse/blow...)
6. Blow out and dry with paper towel.
7. Attach atty to Riva battery and dry burn until you see the coil getting nice and red.
8. Let cool for a minute, prime with about 3-4 drops of
e-liquid and
vape.