Here are a few PAINTER NO NOs for artists attempting to work professionally:
DON'T USE CHEAP PAINT.
I took classes to earn an art based master's degree and my instructor was horrified when I pulled out student grade acrylic paints. It was a popular BASIC line, and I had purchased a package of six fundamental colors. I was irritated and embarrassed, but I now know better. There is less pigment in CHEAP paint. The less pigment means weaker colors that don't mix to create strong bright colors. So it is more advisable to paint smaller and use better quality paint.
THROW OUT CANVAS PANELS
In general, canvas panels that are made with cardboard and sold inexpensively are frowned upon. I have often bought them for children to paint on, and they are great for that. However, they are not considered archival for professional work. You can buy a roll of gessoed canvas and glue cut pieces to a wooden/Masonite backing using artist grade adhesive if you want to paint on a rigid surface.
DON'T EXPECT A MASTERPIECE
When you are at a workshop or a class, it is important to give yourself permission to fail. It is a time to try new things and grow. Don't be disappointed by putting the pressure on yourself to create a perfect image. Allow yourself time to process what you are being shown and realize you will incorporate it into your ongoing painting practice when you return to your studio.
These are all ACTUAL events that took place in my painting career. LIVE AND LEARN!