In reply to subtle:
The most important thing in my experience is to train in open water as often as you can. I didn't.
Don't think simply churning out the lengths in a pool will prepare you!
and practice swimming with others as often as you can - get used to feet kicking close to your face. Agree with start at the back if you're not a strong swimmer and take it steady.
In terms of breast stroke, I had a bit of a shocker in first open water swim tri as had done all training in pool.. a combination of so many people battling for position, murky water you can't see more than a foot in front of you and the turbulence from someone kicking right in front, as well as not being able to see where to go meant I couldn't get into any rhythm going. Practice sighting A LOT!
I started doing breaststroke and actually found it a lot easier... the number of crawl swimmers who must have swum far greater distances because they were zig zagging all over meant I didn't suffer too much. As the race strtched out a bit I got space and settled into crawl.