The Bible says to keep your mind clean, and pure. Using God's name in vain is not. For example: saying OMG, would stand for "Oh my [insert God here]", that would be using God's name as a swear. There are other cusses that are not appropriate for this site that use the Lord's name as a form of a swear.
Exodus 20:7
New International Version (NIV)7 “You shall not misuse the name of the Lord your God, for the Lord will not hold anyone guiltless who misuses his name.
Another example would be to use God's name to lay a curse, doing something that would be against the Word of God, and claiming it is the Lord's will.
Keep your language pure.