Chize0- I've been absent from this thread for a while and I'm not sure how much advice people have offered you, but I'll try to help, too! As for the wig, to prevent tangling, douse it in Motions Oil Spray, which can be found at Walmart in the shampoo & hairspray aisle. Just spray it all over the wig and let it dry before you begin styling. Bangs-wise, tease those babies up! Don't be afraid to attack the wig with hairspray, either; Ariel's bangs need a lot of working-through to get them to stand up. I would also recommend putting some loose curls back into the wig to give it body. Adding a new shirt with poofy sleeves and a bigger bow would help, too! Also, pull part of the hair back into a sort of half up/half down style like it is in the movie.
My all-time favorite Ariel cosplayer is Traci Hines- she does a wonderful job with it. Here
is her Kiss the Girl Ariel costume and here
is a great makeup tutorial that she made that shows a similar look to what she wears when she cosplays. The key to costume makeup is that you wear a LOT. You might feel like a hooker with so much makeup, but it really is necessary to wear a lot. Otherwise, your wig overpowers and washes out your face!
I hope that helped!