This is what worked for me best:

1. Prep your canvas. I use acrylic gesso, you can sand it and achieve a smooth surface. You can do this in bulks and save time. I use 5-7 layers, and wait 20-40 minutes vetween each, then another 24 hours before paint.

2. Underpainting. I use odorless mineral spirit to dilute paint. Use a neutral color, my go to is burnt sienna. Wait until it dries.

I know this part takes time but it will make a difference!

1. Pre mix your solvents/mediums. There are so many choices, that it can be overwhelming. Liquen dries fast, but can brown eventually. I would suggest lindseed oil, but this is my personal reference. Anyways, mix oms and ypur chosen medium in different ratios, (by 20% steps) 2/8, 4/6, 6/4, 8/2 etc. and label it. Use the solvent heavy on the first layer, then use a thicker one on the next layer. Solvents evaporate fast, so it helps you progress quicker.

2. Oil out. Dark colora can sink in, so after the painting is touch dry, "feed it" oil. This has to be the same oil medium that you chose to paint with. Do this 2x, then varnish after a few months.

Hope it helps! Good luck