HIM - Bike aid stations

Practice. I had my kids hand me bottles as I rode up and down the street one day. Just make sure you slow down.  The vols don't want their arms ripped off. I found that 12-13mph was good, but slower won't hurt. Pay attention to what's in front of you. Get the attention of a vol, so they can put it right in your hand. Be out of the aerobars, so you can brake if need be. Thank the volunteers profusely.

I make sure to slow and I'll point to a volunteer so they know I'm coming to them.  That' s honestly the best advice I've ever been given because it works like a charm.  Like wyecrab said, don't be in aero position an definitely practice.  Make sure that after you get the bottle you don't stop or slow down- this could cause a wreck with other behing you.  I usually hold the bottle and ride until I'm out of the bottle drop zone to drink it or put it in my bottle cage.

I've found that some volunteers are better at this than others.  It's hard if they hold onto the bottle tightly, which I've had some of them do in races.  In my last race, the volunteers were great and would hold the bottles very loosely- almost like they were dangling them.  This made it much easier to grab and go. 

Just make sure to pay close attention to the people around you.  Some bottles end up getting dropped and causing bike accidents.  Just go slow, be aware and cautious and you'll be fine

I usually avoid bottle drops in shorter tri's and only use them if it's absolutely necessary.