The above answers have already bit the nail on the head here. But one thing you might want to think about Modally is where the 'Tonal Centre' lies in your progression - basically, which Chord sounds like the chord that could potentially start or end the tune. As mostly any song you hear will have a clear chord that's favoured and returned to, rather than a random generation of chords from the key. Whichever chord from the key you pick to be that chord will change the way that your Scale can be used.
For example you could have these chords from the key of C:
Dm / G7 / C Dm/ G7 C / Dm
In this, we're always leading the ear back to that Dm chord as being the head of the progression, so.this would be a Dorian progression (Chord 2 of the key, Mode 2 of the Major Scale). Technically you could play shapes of the C Major scale over it and it wouldnt sound wrong, but there are certain Dorian tones you might want to favour over others to compliment whichever chord you're on. D, F, A B, C etc)
The same thing goes.for any chord from the key you make the 'Tonal Centre'. You would just use the C Major scale, thinking of it at whichever mode the progression dictates