mysql and php

i was wondering what is the most secure way to use mysql in php. is there a certain way it should be done or a way that is more secure than another? iv'e seen it done many ways and was wondering if it was just preference or a if there was a reason behind it. if you guys could post some examples of how you do it and why maybe you could help me understand or know of an article or tutorial on the subjecti would appreciate it.