I saw ur query and I thought of answering
there are a few things ineed to tell u..
The best thing to do,at least the simplest one is to use the age old technique that almost every body as a beginner uses:
i.)if, u are a good singer(even an average will do) then master the tune vocally........then find the note on which u sustain while singin'...once u do that hum that particular note without changing the feel of it.......if it comes:
A)NASAL u will have to use the minor chord of the note.
For eg. spposing i'm humming a tune and the sustaining note is A if it comes nasal i know it is Aminor
B)VOCAL :that is to say in ur throat u have to use the major chord of that very note.
I hope the example above will suffice for this second instance.
ii.)if u can't even hum that well, then u will have to use alot of concentrtion u will have to catch that sustaining note in ur mind's voice and see wether major or minor suits it..................
iv.)Now here is the bigger problem some times we can't distinguish between nasal and vocal sustaining notes......in that case, adopt the golden 'trial and error method.'
Example:supposing the sustaining note is F# and i can't distinguish between nasal and vocal susutainance I'll have to check it out with both major and minor whichever uits the best...hope u undrstand.
v.) Now an even bigger problem ....this method told above does'nt click always but it is sure to lead u into the scales of the song..here u will have to explore the family chords of the note u found.
If u dont find it there then and ONLY then u turn to any outside help because... music is a very private matter.
Hope this helps u
Genius is in my genes..................................
Conclusion of a particular subject doesn't exist in reality ....
The point known as the point of conclusion is the point where the mind grows tired of thinking any more...................