I follow an American artist named Carol Marine. She's amazing. Carol's paintings are of the "how the hell did she do that?" variety. It doesn't matter what the subject is, she nails it.
One of Carol's key learnings, which has since become a key teaching, is to paint small and often.
The idea is that you can create many small paintings in the same time as it takes to do one large painting, With each painting, you learn something. Therefore you learn more - or more quickly - if you paint small.
She's absolutely right. I tried it and found it liberating to start and complete a painting in one session.
I came to understand colour better when I was using it more frequently and concentrating on a comparatively small image.
Carol's also very big on still life painting, including setting up your own compositions and painting every day objects. This was scary for me but also really fun. I was able to come up with a couple of paintings I was really proud of.
If you are new to painting and just finding your way, I really recommend following Carol Marine. She will blow your mind with her talent and give you practical advice on everything painting related.