A little more advanced method is to look at the shared notes between the two scales you're trying to modulate between (using enharmonic spelling to keep things simple):
G maj: G A B C D E F#
G# maj: G# A# C C# D# F G
So the only shared notes are C and G. Now make lists of all the run-of-the-mill triads you can make using those two notes in each of your two keys:
G major: CDG (Csus2), CEG (Cmaj), CFG (Csus4)
G# major: CD#G(Cmin), CFG (Csus4)
Now look for any shared chords between the two keys. There's only one in this case: CFG (Csus4). That will be your most important one to modulate between the two keys, the 'pivot'.
From here, it's just a matter of playing around with those chords above until you find a progression you like. For example, I came up with this one that sounds nice after a bit of noodling that lands you in G#maj:
Csus2, Cmaj, Csus4, G#maj
Edit: Found these interesting plays on the I V vi IV progression that start in Gmaj and end in G#maj:
Gmaj, Dmaj, Emin, Fsus4, G#maj, D#maj, Fmin, C#maj
If you sub Fmin->Fmaj you get a very interesting chromatic cadence with some delicious harmonic ambiguity:
Gmaj, Dmaj, Emin, Fsus4, G#maj, D#maj, Fmaj, C#maj