Dactylic Hexameter - clarifying rules

Hey there! I just wanted to clarify some rules relating to Dactylic Hexameter. Currently I am working on a 30-50 line poem in dactylic hexameter in English because I wanted to combine my love for writing/poetry & the classics.

As I am writing/editing it, I just wanted to ask about the order of dactyls and spondees. I know that the last two feet are usually a dactyl followed by a spondee. But for the first four feet, what are the general rules? Do they ALL have to be dactyls or can you have spondees in the mix as well? Any help is greatly appreciated! Thanks.