Please, please, please detangle your hair before you let any water touch it! Pppplllleeeeaaassseee!!!!!!! Else you will end up with a tangled, matted mess! I speak from personal experience!
First detangle with your fingers, making sure the strands aren't interlocking with one another. Then comb, comb, comb!!!! I don't know what kind of braids you have, but please work one braid at a time regardless.
Something that I just learned (from my beautician no less, I don't know why the ***** didn't tell me this when she first started braiding my hair 3 years ago!!!!) drench your hair in conditioner and either keep it on over night or several hours. That was the best thing I did and I did not get one single knot or matted section once I washed my hair. I just used some extra conditioner I had on hand not my good expensive stuff though.
Some of the ladies on the board talk about using a spray called Unbraid something or other but I haven't been able to find it anywhere. It is supposed to make taking done braids easier, they just slide right off. Me, I just unbraid.