First you want to decide on the wedding and if it is going to be formal or more casual. For instance if you are having a very formal wedding and you wear it too loose it may come down and look tacky. But it you are in the backyard and it falls down then it will fit into the situation just right.
Another thing you need to consider when choosing a hairstyle is the weather conditions. If your hair gets frizzy in hot weather then make sure you do not wear your hair with large loose curls because it will not stay that way for the wedding. This would be a good time to wear it up.
Hair length is another consideration but when you have medium length hair it makes it easier to do just about any style for your wedding. The most popular style for medium hair is the half up look. You can find many variations to this style so choose the one that fits you the best.
Remember there are many hairstyles to choose from so make sure you check out all the latest trends. You want to choose a style that fits your particular style.
Source : http://ezinearticles.com/?How-to-Choose-Wedding-Hairstyles-For-Medium-Length-Hair&id=2428765