When running away from the cops, you will have a circular area in which they look for you. However, if you get out and another cop sees you, it changes. To use this to your advantage, barely get out of that circle, which you will see on your radar. Then, just sit there for about five seconds instead of flooring past it.

If you are at a four star wanted level or less, find a place with grass or sand. The cops will follow you in, but they usually cannot get back out. You can then just drive away.