Just take your time. Use good magnification. And remember that not all gems are going to show interference.
What sort are you using to practice with? How are they cut?
The colors show up around the optic axis of a stone, so a lot of times you can see it through the girdle or long axis of a cut stone. If it’s an issue of not being able to see what’s going on inside because of all the reflections, submerse it in water or oil and all the exterior reflections will be masked.
Also, I recently found these two resources online that explain a lot about how this stuff works, I haven’t read in depth but I’ve learned a a lot