You may have experienced this: you do your makeup, everything is lovely, and then, BAM!, you have a streak of color in a weird place on your face. How did that happen? Here are a few things to watch out for.
Taking care of the fall out
In keeping with a recent blog entry about using a light touch when applying makeup (see http://celestesmakeupcorner.blogspot.com/2012/08/light-touch.html ), first off, you need to use dabs or pats when applying your eye shadow on your eyelids. That being said, even with this application technique that will help you tremendously get rid of major fall outs, some fall outs can still happen. The worst thing that you can do is to try to make it go away by using your fingers: that will only embed the eye shadow more into your pores... it's tricky that way. Instead, you want to use a fluffy brush (e.g., kabuki brush or powder brush), ideally one that you have used with loose powder as that will help replace the eye shadow specks with powder. You can use just a fluffy brush to brush down the fall out... but if it's stubborn, just go ahead and apply loose powder. And, when using this brush, use a light touch, again, to prevent from embedding the specks in the pores.
Also, do it pretty much as soon as you notice some fall out. Otherwise, you run the risk of unknowingly spreading the colored specks all over your face.
Keep your hands clean
Periodically, while applying your makeup, check your hands. They sometimes will get some fall out on them or they will have gotten some product on them that may contribute to a (not so beautiful) streak on your face. When I apply performance makeup, I end up washing my hands a good 3-4 times because of that. If you're applying your makeup in a dressing room, make sure that you have makeup towelettes handy so that you can use those to wipe your hands if needed.
Keep your containers clean
One thing that contributes to fall out and streaks quite a bit is dirty containers. I keep my makeup at home in a chest of drawers (yeah, I have a lot... it's a small furniture thing but still) so they're always upright. When I'm travelling, I'm also trying to keep my makeup upright. When I'm unsuccessful, that's when the products start escaping their pots and there will be colors around the containers. If I notice that the containers are dirty, I'll use a tissue, paper towel, etc., to wipe the exterior of the container (and my hands).
Mascara mess up
If you have had a mess up with your mascara where you fumbled with the wand and it went flying somewhere where it wasn't supposed to (happens to the best of us), wait for it to dry, then gently rub it off. The funny thing about mascara is that, if you try to clean it up, it will smear and make a bigger mess whereas, if you wait for it to dry, you can rub it off with your finger (even if it's waterproof).
Try not to use makeup remover
Unless you really messed up a lot and it can't be fixed, try not to use makeup remover to clean an area. The reason is that, suddenly, you'll have a spot that will be a different color than the rest of your face. You really can't just remove the top layer of your makeup: it will ALL come off from that one spot. So reserve that for a really messy spot. I think that I can count on one hand the number of times that I've had to use makeup remover. Try the other techniques first. The only caveat is that, if you're using a liquid liner, you may need to use makeup remover if you mess up. It's really hard to correct.