Here is a simple step-by-step tutorial to teach you how I create glowing objects in my drawings.
The key to getting a nice glow effect is using blend modes. The two blend modes I use the most in my art is "add" and "pin light". There is no rules when it comes to using blend modes, you just have to play around with them to see which effect you like best.
Some examples of the glow effect in my drawings:
I typically draw stars, but you can create any shape you want in your own drawings. You can also use any color scheme you want, as long as the background is darker than your glowing object/glow effect color.