you want to drip onto the cotton or it will flood, depending on what you're using to drip from, on my innokin ucan with a needle tip i usually do 20-25 drops, from a more typical bottle i do like 16, 20 usually makes a mess lol
how much juice you can drip at one time really comes down to how you wick and how much cotton you use though, and most people will tell you less is more in that department. do a search on youtube for leo s wicking tutorial, or i think that style is also called roller coaster wicking, that's how i like to do mine, but there are a lot of different ways, watching video tutorials is a good way to get ideas and see what works best for you