Well, I am a sculptor who paints, and I'm married to a portrait painter, so I admit I have an advantage there. Years of practice, study, and developing techniques. Everything we have learned has been by study and practice, and is not beyond others to learn, believe me. I managed at first with very little knowledge, by cautiously following these basic rules. My top tip would be to use very thin layers of paint, never thick ones. Work gingerly, especially as a novice. But work rapidly, without fear, and with large, long strokes. Use a big brush, not a small one. If you're about to try something new, Practice off the model. Learn about wet in wet, drybrush, and scumble. Acrylic paint can be moved around or washed off before it dries, but even after drying it can be cleaned up. Definitely practice off the model until you have built up some skill and confidence. The best advice is to use thin paint. You should learn the difference between opaque, semi-transparent, and transparent paints, and use each according to its own characteristics and limitations. I prefer to avoid opaque paints except for small details at the end, then on small brushes. Create a good all over painting surface by spraying with a grey primer. A quick, thin spray coat is best. Next build up thin layers of transparent or semi-transparent washes or glazes. Start thin and you can always make the colour denser as you become more confident. When thinning acrylics, use medium, not too much water, which weakens the adherence of these paints. Don't be afraid of using large brushes. Don't be afraid of so-called accidents. You can work unexpected results into your weathering. You can fix or re-do anything if your paints are not thick and glommy. Practice until you are fairly certain of what you're up to and proceed with confidence. The main thing is to dive in!
Spray painting is an art as well, but not a hard one to master. I only use it for my primer coat anyway. Shake the can, start the spray beyond an end and sweep along, finishing beyond the other end. Don't stop moving your spray can. You are aiming for a thin smooth homogenious coat. Don't re-spray unless necessary, and then only when the first coat is absolutely dry. KEEP IT THIN !!!!
Cheers!