Modulating is extremely gratifying and can bring much audible pleasure to the audience. Mastering the fine art of modulation requires a certain musical background, but today I will show you the way that I would do it with the use of tonal center.
The secret is to find common notes to the 2 different modulating keys. Once a note is found, we'll find the relative modes to the original keys, and bring them to their relative modes starting with that common note.
Here's a practical example. We'll improvise over the keys of C Dorian to C# Dorian.
Analyzing these two keys, we find that both of these scales share the common note of Eb
Bringing these 2 keys to their relative Eb mode, we'll get:
C Dorian = Eb Lydian
C# Dorian = Eb Phrygian
Now using these two modes starting from the same root, we'll be able to create interesting modulating musical ideas.