Another thing a lot of people don't know is that some of the progressions repeat across keys.
A 2-5-1 in C, is a 5-1-4 in G.
A 7-3-6 in C, is a 3-6-2 in G.
A 1-4-5 in C is a 5-b7-1 in G. (kinda weird, but you can do it)
A passing chord that you'd use on the 5 in C, can be used as a passing chord to the 1 in G.
A passing chord that you'd use on the 2 in C, can be used as a passing chord to the 5 in G. (makes the Dmaj stand out more, because you're playing a minor before it)
These rules repeat for a lot of the intervals, and they also work with scales. Try them out!
The chord and scale rules are a little more flexible than the progressions. You can even substitute a lot of the chords or scales that you'd normally play for a certain interval over another.