Aways verify your program and offsets using single block and low rapids to make the first part, once the program and setup is proven you can let her rip. Develop work habits so that you always do things in the same order. For example I always load my tooling first, set my work coordinates second, and set my tool length offsets third, I'm less likely to forget something if I always do it in a certain order. Also when using single block and low rapids be sure to check your distance to go display, if you know your endmill is supposed to go to -.250 and you see the distance to go showing -2.5, you know you are gonna crash. Here is a link to an article that may be of some help to you.
http://www.mmsonline.com/articles/cnc9810.html