Clinginess sends a message to your boyfriend or girlfriend that you can't live without them and that they are the center of your universe. This gives them total power over the relationship and over you. Not to mention, being clingy comes off as being needy and is a real turn off. There are ways to stop yourself from being clingy in a relationship.
Understand that other people have lives outside of yours. When you think everything you do is at the center of everyone else's universe, your insecurities become annoying and people get tired of reassuring you all the time.
Be understanding of another person's time. A big mistake that makes people appear clingy is to try to dominate another person's time. Don't expect the relevant individual to spend every spare minute of time they have with you.
Try to stay off the phone for hours on end with your partner. Limit your phone calls with them. Calling someone all the time and not letting them off the phone easily makes you appear needy. People will look at their caller ID to see if it is you calling. If you find the person you call all the time is suddenly not answering the phone, this might be a clear sign that you're calling too often.
Go out with friends in social situations without your significant other. Encourage your partner to do the same, making sure to remove all signs of jealousy. Being independent outside of your relationship shows an attractive level of self-confidence.
Find something you enjoy that you can do outside of your relationship such as a hobby or sport. Take an art class or sign up for your church's softball league. This will help you prevent making your partner the center of your world.
Be yourself. Try not to be so apologetic about everything you do. This makes you appear needy and that you have a perpetual guilty conscience. You don't need to be a perfect person for someone to love you and want to be around you.
Feel secure with yourself, believe in yourself and know you have great worth.
Don't ask your significant other's permission to do things. This comes off as clingy behavior because you "need" their acceptance and approval before making a move. Your partner should never be the only thing in your life that makes life worth living. That's too much pressure to put on a person and you will most likely eventually loose him or her because of it. If you put someone up on a pedestal, chances are they will take you for granted or eventually take advantage of you.