I'm going to touch on the top five makeup mistakes that I see, and give you some suggestions to correct them. One of the biggest ones would be misuse of bronzer. I would say definitely use bronzer to accent your face. Do not just put bronzer over the entire thing. It's just too one dimensional. You're going to have a line here, and it's not going to match your neck so, don't misuse bronzer, please.
The next one is not blending. You really want to blend everything. Eye shadow, blush, bronzer everything that you're using you want to make sure is very well blent[SP]. That includes using the correct brushes. So, make sure you have good quality brushes that clean. An easy way to blend would be to use a setting powder, and a nice Kabuki brush. You can just go ahead, and sweep over the entire face. It's just a quick easy way to blend.
One of my next tips that I see people complain about would be having their makeup fall off throughout the day, or slide around, or it just doesn't look as good. Basically the solution to that is use a primer, simple. They have eye primers, face primers, there's setting sprays, stuff to increase the longevity of your makeup that will definitely help.
So, one of the next makeup mistakes that I see is using a brow color that's too dark for your eyebrows. I actually say go slightly lighter than you would think, because when it's concentrated within your eyebrows it will come off darker anyways, but don't go too light. Don't take that to the other extreme, but definitely if you've got brow color similar to mine you don't want to be using black, because that's going to come off too harsh.
The last one would be don't be afraid to use color. I love a nice pop of color here and there. I like a nice flush on the cheek, a fun lip color always brightens you right up if you don't have a ton of eye shadow going on. Just get a little pop of color in there, and don't be afraid to use it. Those are some solutions to the top makeup mistakes.