Some things respond better to sublingual administration than others I haven't done it personally with Adderall so I can't comment on that. Generally you just need to hold it under your tongue until nothing remains. I generally consider it a success if you don't end up tasting whatever it is you've put there (tastebuds are mostly on top of your tongue).
A few days ago I'm certain someone was trying to explain to me the optimal place in the mouth for absorption, but it escapes me. I'm pretty sure it was towards the back of the mouth involving the gums although don't hold me to that. I tend to do it off to one side about halfway down where you can see the veins, I can't comment on whether this is a superior place to anywhere else under the tongue really.
EDIT// Somethings just seem to force you to salivate and make it v. hard to keep underneath whereas others will stay pretty dry.