The best modulations are often the ones you don’t notice, unless you want a dramatic effect. There’s so much theory on this. Alan Belkin on youtube has excellent Classical music theory videos. He goes from basic to very advanced. There’s tons of other videos on basic stuff, but Dr. Belkin is really great for all aspects of music, harmony, melody, orchestration, composition, etc. .A grounding in “that stuff” is important for anyone trying to “learn Scaler.” 
For me, it does all come down to what you can actually hear and learn to hear better. Make a list of songs that have what you think are chords or modulations similar to the ones you’d like to use. All the pros talk about the importance of transcription and I concur with them on that completely. Try to figure out the chords by ear.
Here’s one workflow I’ve been using with three instances of Scaler.
The first is the Master which contains the primary Patterns.
The second is called “Modulation” this contains the “pathway chords” to the next section.
The third instance is usually called, “chorus” or “B Section.”
With this set-up, I have the start of the piece in the Master instance, then, a Scaler just for modulation. This lets me try different chords in a more organized way.
The Third and subsequent instances contain whatever comes next.
This may not be the best way to do it and it is certainly not the only way. It’s a workflow I’ve been trying and it seems to help keep Projects organized.
Take care.