When I have some free time, I like to watch art technique videos on YouTube and one of my favorites is Jane Davies.
She offers paid online workshops as well but, her long list of free YouTube videos are extremely helpful and cover a wide range of topics. She focuses on everything from mixing colors to collage techniques to mono printing. Her medium is mostly acrylics and her style is very free and abstract. I like how her videos are simple and easy to follow.
Even if your style is not the same as hers, there's a lot you can learn from her about simple techniques that can be implemented to create texture and variety in your work. She also gives great advice on the basics of good composition and how to use a variety of tools in creative ways. I often use her suggestions as a way to warm up when I first get into the studio.