An hour ago I was having a harmony review lesson online with Victoria who is my student from California.
We were discussing things like harmonic progression between tonic and dominant and vice versa and tonic and subdominant and vice versa.
We did the most simple keys, like C major and A minor.
Victoria understood that she also needs to work on other more complex keys with more accidentals.
So for this we refreshed the concept of the circle of fifths.
At some point our discussion went to minor keys and how to find them from the major key with the same number of accidentals.
You need only to take the first scale degree of the minor key and go 3 steps upward to find the parallel major (an interval of minor third). For example, F minor and Ab major or B minor and D major.
It's opposite, if you want to find minor from major key.
Go 3 steps down from the 1st scale degree of the major key (and interval of minor third). For example, F major and D minor or Db major and Bb minor.
Hope this helps.
[Thanks to Victoria]