Think of something funny. I don’t think it’s something that can be avoided.

I have been turning red my entire life. There is really nothing you can do to stop it.

You can lessen the times you will turn red. You could think about things that have caused you to turn red in the past and keep thinking about them until you have no reaction in the mirror.

Apparenly wearing a moisturizer with a green tinge will help disguise the redness but I think that is just for more permanently red skin. I blush all the time and most people I have spoken to actually find it attractive. Blush with pride, giggle at yourself in those embarrassing moments and it goes away quicker. If you get embarrassed when you blush you end up blushing more, thats all I can recommend.

I don’t think there is a way to prevent it. Its a uncontrollable physical response. I may sometimes joke people who do blush, just to see it happen but I actually think its cute. And certainly nothing to be ashamed of.
There may be a few times where I can see it would be a problem because it may lead people to think you are attracted to them when it may be something they just said or a look they gave you that makes you feel uncomfortable. But I like to think of a person blushing as someone who simply hasn’t learned to hide their, fears, or embarrassment or awkwardness. Someone who is still very real and not jaded by life yet.
Once you become jaded it will be easier not to blush. But don’t hurry. It will happen all on its own without you trying.

Talk to your doctor if this is seriously affecting your life. There may actually be medical help for you.

I posted this once before for the same question. I really think this girl has some good sensible advice. Good luck!!!
http://www.youtube.com/watch?v=bUjBr20kl20