I have some tips for you, coming from an illustration background. You can see some of my work here:
https://shirajg.wordpress.com
Try charcoal and a white pencil on toned paper at first. Work from dark to light, applying large areas of tone with the charcoal, then picking out light shapes with a kneaded eraser, and finally adding highlights with white. This is a lot like what you eventually do with paint.
When starting to paint, use oil paint, or acrylic with a retarder in it to slow drying time. This will give you a lot of freedom to fix mistakes.
Work in layers when painting. This can let you tackle different aspects of the painting independently. You can start by toning your painting surface to a base color, then doing a sketch on top of that to establish the big shapes and edges. Once that's dry, you will always have the underdrawing to help you along as you paint. If you screw up the painting, you can scrape off the paint and start from the drawing again.
Learn to see values. The best way to do this is to squint. You'll see obvious contrasts in the light and dark, these are the values. All the detail within those values needs to sit very close to the value it's within. It will seem like there's a lot more contrast when your eyes are wide open and you're focused on one area, but you'll lose the gestalt effect of the light if you do that.
Work your paint from thin to think. You can be more sketchy and loose with thin, flowing paint. Save the thick stuff for the end, when you're sure everything is in the right place, looking how you'd like.
Learn to mix colors to a target value. Pick a random color and paint a swatch of that somewhere, then take another color and lighten or darken it until it's the same value as the first swatch. You can test how close you got by dabbing a bit of the new mix into the swatch you painted before. If the value matches it should fade into the swatch pretty seamlessly. If there's contrast between the dab and the swatch, the values is too light or dark. Do this enough and you'll be able to eye it.
If you want to paint figurative works, learn to draw.
Learning the 3D form of objects is of great help and should work in tandem with the visual stimulii you are observing.
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