How can I improve my painting skills?

I recommend studying colour theory, anatomy, and perception.. But do so at your own pace.

A really good exercise is going to your local zoo and visiting your favourite animals. Do quick, unrefined sketches to practice gesture and the use of negative space.

Another good exercise for practicing technique are cloud studies. Give yourself 10 minutes to render a sky with clouds. The time restraint will allow you to develop your observational skills as well as your finesse with the brush.. (Dont forget to try and use all sorts of brushes to see what works best for you!)

Most importantly though, just keep going!!

Take some classes at your community college and paint a lot in your free time. Buy some books on painting and practice the different techniques they introduce in the books. If you have access, try and find Bob Ross's videos. Honestly, he is what got me into painting at a very young age when I watched his show. That's what I can offer. It's all about practicing the techniques you learn from any source.

Well, the first thing I would suggest is practice. If you paint a lot, you will (most likely) get better from experience. You could also take a class, but that costs money and takes time. If you know anyone else who likes to paint, you could talk with them and exchange artwork and techniques and learn from them.

Check out art museums and see if you can get permission to practice sketching the art. Best way to learn from the masters.

Also, read and learn about the Golden Rectangle, and other ancient discoveries based on math( you may be surprised!).

Practice of course. But try new techniques or styles. So if you paint realistic, try something like impressionistic or abstract. Venture out of your comfort zone. You can even try taking courses in different styles.

Have the courage to not try to do anything.

"Only when he no longer knows what he is doing does the painter do good things." - Edgar Degas

Practice, practice, practice.