Friends do grow apart, it is nature's way of saying you weren't meat to be. Life has it's subtle way of showing us things, so it's our job to listen.

  If you feel like you are growing apart or simply never had the connection needed to sustain a valued relationship with a friend then simply let nature take its course. Don't return every phone call, after all, you don't feel like talking to that person every time they call. If they ask you to go out somewhere with them, simply tell them the truth, you don't feel like going out with them. If they continue to try and pursue a close connection with you and you don't want to feel like you are leading them on in some sort of way, then simply tell them. Just explain to them that you do not see your friendship amounting to anything positive in the future, and that you would like to pursue other things. If they STILL continue to try and pursue friendship, give them a few more chances to get the idea and then call the cops.

 Now, with all that aside I will say for some instances it is very hard to rid your life with certain aquaintences. For instance, the "friend" you are growing apart from lives next door, or that person might be a family friend. In these cases it is best to just do the subtle things like not return phone calls and so forth. You want to rid your life of them, but keep it professional, some people we just have to learn to live with (Like Uncle J.Doe who smells like beef and burps up Miller Lite) .

 Keep the good friends you have, the ones who have your back and stand beside you. Rid yourself of the ones who question your good decisions and who complicate you bettering yourself .  Act like you know it.