forget the hair styling products and/or get a 3/4 helmet
Keep it styling product free, i.e. no hair spray, mousse, gel, decoupage or paste. It just makes it worse. Blow dry your hair before starting out, it will give it some extra body for later. Keep the helmet vents open to limit sweating. Carry a comb with you (one with the two different lengths of teeth and the teeth on the comb should not be really fine toothed). When you take your helmet off, bend over and comb from the back of your neck to the front, you can also use your fingers but a comb gets down to the scalp better, this lifts the hair. Then from the front you comb out the sides and bangs up and out away from your face and scalp, this also helps dry the hair, once the sweat has dried some you can use the comb to style the front thus eliminating bad helmet hair.
I also got a perm to help with the body and carry a pick so that if my hair is sweaty I just scrunch it up and it recurls quite a bit. I love styling my hair and I like barrets and pony tails and clips and such, so carry a clip in your purse and twist you hair up and on top of your head after removing the helmet this hides some of the flatness and then just quick poof up the bangs. Barrets are painful with a helmet as are most hair accessories, french braids and low ponytails work if you have long hair, mines in between so it doesn't always work for me. I also don't wear a full face helmet due to claustrophobic tendencies, the helmet I have is a 3/4 with full face sheild, which goes on a tad easier and doesn't push and pull my hair every which way.
I remember years ago there was that one commercial where the sexy girl pulled off her helmet and her hair just cascaded out and was full of body, and styled, no helmet hair at all, if that is what you are looking for just forget it not ever going to happen. Be realistic and know that you are just as sexy as that girl, you ride either on the front of the seat or the back and are willing to be seen at your not made up best, and in the long term you saved your self hours infront of the mirror, which gave you more hours to ride, and saved lots of money not purchasing hair products.
ps. my 17 year old daughter is going to motorcycle class this weekend so here is another lady in the making who wants to ride and she wears her hair short so she just shakes her head when she takes her helmet off.