There are just infinite ways of doing it. But certain things work better for certain kinds of music. I mean, if we're talking pop music or country music, half step or full step mods are appropriate and expected. For jazz stuff though the sky is the limit. Just listen to a few of the old pop and bigband arrangements from the 40's, especially those with vocals. The vocal chorus is almost never in the key of the instrumental, and you can find some really neat ways of worming your way around from key to key by studying those.

Some examples, let's say you sing a song in C, for ease of thought. But, for instrumental ride you modulate. Where to? Any key is possible. Everybody knows how to do a whole step or half step mod up. so let's examine choices apart from those.

C to Eb. Well, you can go C, to Fmin, to Bb7, into Eb, just following the circle of fourths. Or, try a walkdown. split bar C to B7 to full bar of Bb7, into Eb.

C to E, just a walkdown from C to B7 to E.

C to F should be pretty easy to come up with, as the keys are in the circle of fourths.

C to F#, C to C#7 halfstep mod into F#.

C to Ab, Half step mod from C to C#, treat that as the 4 chord of Ab, then Eb7 to Ab. Or follow the circle, split bars C to F7 to Bb7maj or min, to Eb7 to Ab. So on and so forth.

There's almost always a musical way to get from one chord to another. If you can't find a chord progression you like, look for melody lines that make sense and suddenly the chords will sound a lot better. Pulling off a successful mod often has as much to do with the right hand melody line choices during the transition. For instance, if you're trying to get from C to A, and you don't want to go down a half step to Bmin to E7 to A, but just going from C to A sounds dumb, then tri to find a melody line in the right hand that makes it work, maybe focusing around an E note during the transition, because E is a shared note in both C major and A major triad. The 3rd of C and the fifth of A, so putting emphasis on that common tone will draw the ear to that and away from the slightly awkward chord pattern.
Or, another way to get from C to A would be C to E to A for chords. And to make it sound smooth and flowing you can play a G in the right hand over the C, a G# over the E7 or E maj, and an A over the new key center. So suddenly your jumps from C to E to A sounds like a nice chromatic line because of what you did in the right hand.

Hope that helps folks think about key changes in new ways.