If you get meat birds, get chickens that all pretty much look alike. If you can't tell them apart, you are less likely to see individual personalities and quirks that will make you attached to them. By that same token, don't name them. Very few people can bring themselves to eat something they've named. Take care of them--feed them, water them, clean their coop and run, and handle them enough that they are reasonably tame, but don't cuddle and play with and baby them like you would your other chickens. If after you do all this, you still have a chicken or two that stands apart from the crowd, don't feel like a failure if you decide to keep it aside as a part of your permanent flock (Assuming it's a variety that can thrive--some varieties bred for meat don't live long regardless of what you do).
I've never raised meat birds before, but I have a lot of experience with avoiding attachment to animals if I know they're not going to be in my life for very long. It's a tricky art to care for an animal, give it all the love and care it needs to thrive, and do so without becoming emotionally attached to it.