I used to blush A LOT, for something as small as just a girl I didn't really know talking to me. It was always loads worse when someone goes "OMG HES GONE SO RED!!" and then someone else pipes up "HE FANCIES YOU" kind of thing, making it altogether much, much worse. That was up to the age of 14...from then, someone talking to me wouldn't make me blush, but even recently I was amazed because I blushed just when some girl started asking me something kinda random, maybe about siblings or something. I was only embarrassed about blushing, nothing else, god knows why it happens.
That is unusual though, but I'm blushing just thinking about it! Normally, I will now only blush if lots of people start looking at me, or if I feel embarassed. So my point is, just talk to people and so on, encounter as often as possible situations where you normally blush, and it does to a certain extent get better. As well as that, advertise the fact that you blush, tell people before it happens, make a funny story "it's so annoying, I blush even when I'm not embarrassed, that makes it embarrassing!" kind of thing; then it doesn't feel so bad when it does happen.