The custom is to wear 2 tzitzis in front and 2 behind in order to be surrounded with mitzvos. One should also be careful that the same 2 are always in front (this applies to the talis katan and gadol). However, the Arizal was of the opinion that these 2 do not always need to be in front.

There is a big discussion in the Poskim regarding wearing the tzitzis strings in or out of one’s pants, and therefore each person should ask a Sheila about it.