1. Basically the first thing that I do is decide what spectrum of colors to use. Whether I want my painting to have a dark cold/warm theme, or a bright hopeful theme. When you have an understanding on how colors will look when painted together on canvas it will be much easier to begin.
2. Block out all of the colors that you think you will be using on the canvas. Just color them in as you see fit (you will be painting many layers here so don't worry). As you paint you will learn how certain colors look painted on top of black, or how the colors will "pop" off of the page.
3. Don't use just basic colors. Mix a little blue with your black, or some red to create a subtle red effect showing through once the black dries.
4. Go light at first. The more acrylic without water then the more glossy and less opaque your paint will dry. You can dilute the acrylic with water and have it work for you as a water color will.
5. Don't be afraid to try something new. No you can't erase, but you may always cover up sections and repaint it.
6. I know in my experience I will add to my painting until I either come up with something awesome or straight up ruin it. Know when to be content.
7. Never finish the painting in one sitting. After staring at any object for hours on end you start to look to deeply into it and will almost always get frustrated when you can't figure out what is missing. Work on it in stages. I always do my basic layer and a little more. Then I will set it in a place where I will see it in passing throughout the day. A day or two later I magically know what it is I need to add or remove. It is amazing and you can continue your painting with a clear un-biased mind.
8. If painting on a Canvas surface, use a gesso as a prime layer before you begin. Wait for it to dry and sand the surface down to be very smooth. This will give you a wonderful surface to work your acrylics into.
9. It's good to be critical of your own work, but understand that painting is not a skill you are just instantly a pro at. It takes time to learn how everything will look once it is dry, there are many brush techniques that I will cover in another post. Also be able to take criticism, it will only make you better.