I have been to a few myself, including workshops from Jacobus Baas, Erin Dertner, Corrine Hartley and Greg La Rock. Although they each have their unique style, they all teach the same basic points which are composition, focal points, creating a pleasing flow in the painting, values
and the use of color intensity.
Don't expect to go to a workshop and come out painting like the teacher. But, you should challenge yourself to try new and different methods. Try their color mixes, brush or palette knife techniques, canvas etc. You may or may not add it to your repitiore, but you will learn or re-learn the the same basic points seeing them in just a different medium or technique.
Also choose a teacher who talks a lot while they demonstrate. It is lovely to watch some one paint , but if you do not understand what they are doing it will not be helpful.