1. Count the number of accidentals and remember the circle of fifths (e.g. if you see 2 flats it can indicate Bb major or G minor key).
2. Look for the signs of harmonic or melodic major or minor mode (e.g. if you see F# - that's the sign of harmonic G minor just as Gb is the sign of harmonic Bb major).
3. Look for altered scale degrees (e.g. II-, II+, IV+ or VI- in major key or II-, IV-, IV+, or VII+ in minor key).
4. Look at the closest cadence and think what scale degrees you can see in the bass. Usually the cadence ends on the 1st, 4th, or the 5th scale degrees of the key).
5. Try to identify some basic chords, such as tonic, dominant or subdominant and their inversions.
Keep these points in mind when analyzing modulations to any keys in organ pieces that you are playing. They will help you to understand not only the structure but also the tonal plan of your compositions which in turn will make your playing more meaningful.
Transposing Sequence in F# Minor: iv-ii65+-V-i