Hi , how do you know what minor chord you can add to a chord progression , of 1 ,4 and 5 chords , i know am is included in anything with C,F & G , which is almost every song ever written 
but any help would be gratefully appreciated , ive been googling , but just end up confusing myself 
thanx
The chords in every Major Scale go like this Major, minor, minor, Major, Major, minor, Diminished.
In the key of C the minor Chords would be Dm, Em, Am.
Am is included with C, F and G because it is the 6th and the 6th is the most common chord added to a 1 4 5. So if you change key to G the 6th is Em. Write out the chords in the Key any song writen in and it will help you figure out what minor chords will fit
The 2nd is also a common minor chord in 1,4,5 progressions.
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Here’s a table of common chord progressions I recently made. I pick one and practice my barre chords with it. Where I know the key of an example song I’ve put it in the correct box. If I don’t know the song’s key I’ve put the left column. If you know the key of the songs in the left column, let me know.
I’ve used digits for the chords instead of the more common Roman numerals. The 2 & 6 are in smaller font to highlight that it’s a minor chord. It’s a work in progress, so happy to hear constructive feedback.
Think I might have the b6 chords wrong. They should probably be flattened minor chords whereas I’ve got them as flattened major chords. Can anyone clarify?
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Thanx very much stitch , big help 
Big Thanx for that jack , really helpful
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The answers and tables you’ve been offered are great.
For long term and deep understanding you could try this:
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