Painting in layers
If you like to use pencils in a drawing, adding layers of paint slowly can take a sketch to a stronger original piece of fine art. Pencil can create tones and shadows and are much more precise than paint strokes (unless you're at a level of Van Gogh which.. we can all dream). Adding a layer of paint one by one - gouache works well - you can strengthen the parts of your sketch that you like and fade out anything you aren't so happy with. Here is a picture of this process of the first layer of Cacti Rose which I used this technique for.
After getting the tones that you want, you can start to add colours and details, which is terrifying because you have no Command+Z button.. but fear not, it takes lots of bad art to make any good art. I had to really think through the colours that were added to Cacti Rose, rather than throwing any colours onto it. It meant selecting a broader colour scheme to the painting. Each painting is a real learning curve, I am pretty sure this is why we create things; it helps us to process by doing. Whether it's writing a song or learning a new computer program, the best thing is to get started!