setting fence posts

When installing vinyl fence, or any other type, how would you layout posts?

Can I dump my pre-mix concrete in post hole or must I mix it first? Customer Question: My question deals with setting 4x4 pressure treated fence posts with concrete. I was wondering how important it is to mix the "pre-mix " concrete before I set my posts. I would like to take the easy way out and just add about 80 pounds of pre-mix without mixing it. Does that sound acceptable? I'm planning a 6' wood fence in a mountainous environment 8200' elevation with typical wind loads for that elevation. Please let me know what you think.