You can't just play G Minor over a progression that is in G minor. Well I suppose you could, but you'd be taking a risk
A safer bet would be a G minor pentatonic, because it does not include any of the characteristic notes of any minor modes. An even better bet would be to find out the chords!
Here's an example, you are playing in G Major but you're unsure of the chord changes. You decide to play G Lydian, which is G A B C# D E F#, all the sudden your Lydian sounds like shiat!! Oops chords changed to a IVmaj7 chord (C major)!? You're screwed and sound like an idiot
This really depends on the tempo, if the chord changes are going really slow you *might* be able to get away with G lydian over the G Major chord and have the C major sound like a modulation, but you better not play C# during the time when the bassist and keys are playing C major!
So here is some basic info to get you going.
Ionion is Major
Dorian is Minor
Phrygian is Minor
Lydian is Major
Mixolydian is Major (Dominant)
Aeolian is minor (natural minor)
and Locrian is half diminished.
now you want to learn the characteristic notes of each scale. Which notes define a mode? What makes Mixolydian different than Major? well mixolydian has a b7. That would be it's characteristic note.
characteristic notes get a *
ionian 1 2 3 4 5 6 7
dorian 1 2 b3 4 5 6* b7
phrygian 1 b2* b3 4 5 b6 b7
lydian 1 2 3 #4* 5 6 7
Mixolydian 1 2 3 4 5 6 b7*
Aeolian 1 2 b3 4 5 b6 b7
Locrian 1 b2* b3 4 b5* b6 b7
You already know the chords that can be built off a major scale. You can use that to alter the scale degrees to go along with the different major modes! You also want to be familiar with the chords for a natural minor scale (aeolian) so that you can alter them to corrispond with the different minor modes.
So here they are:
Imin7 ii-7(b5) bIIIMaj7 iv-7 v-7 bVIMaj7 bVII7
subsitute a V7 chord for v-7 for harmonic minor (and raise the 7th degree of your minor scale to a natural 7)!
Hope my rambling made some sense for you
Good luck, remember to let your ears make the final decisions!