Can I swap SIM card in iphone 4s into 4?

I just dropped my iphone 4s and the screen/display is no longer working. The rest of the phone works and I was able to back up. I have an old deactivated iphone 4 that I can use. I want to know what steps I need to take to get the 4 up and running (i.e. How to activate). If there's a detailed set of instructions on the web you can point me to that would be great also.

Restore the 4 off the 4s backup in itunes and pop in the sim card.simple

It would depend. Does the iPhone 4 take a regular sim or a micro sim card?