Aw, thank you so much!! Hmm right off the top of my head, the following is what I wish I knew before starting watercolor (in no particular order):

1. Buy the best quality materials that you can afford!! I can never stress this enough, but painting with good supplies will tremendously aid you in painting. Painting is hard enough as it is, so spare yourself the headache that inferior materials will give you. You don’t need many supplies, so I’d first buy a decent brush, then a pad of paper, and then maybe four colors (a red, a blue, a yellow, and a brown). Any non-porous white surface will suffice for a palette, like plastic or porcelain. I usually use empty plastic containers to hold water (like gelato containers that I’ve washed beforehand or a water bottle that I’ve cut in half with scissors). Also, don’t forget tissues!! They help moderate the amount of water in your brush, and I cannot imagine painting without them :)  For more info, I also sometimes post art supply reviews on my website, and I have suggestions on what to buy for watercolor classes over here. 

2. Buy single pigment colors!! On the paint tube label, it should say which pigments are in the tube. If not, don’t buy it. Ideally, it’s usually better to have one pigment in each tube for cleaner mixing (with some exceptions). Pigments are coded a standard way, but color names are not. For example, Ultramarine Blue is PB29. The P stands for pigment, the B stands for blue, and the 29 is the number assigned to that pigment. So some companies might name it “Sky Blue” or “Ocean Blue” or whatever, but if the labels all say PB29 then they’re all the same thing. Handprint.com is the best resource on the Internet for learning about different pigments, but if you’re just starting out don’t stress too much about it! 

3. Take care of your brushes!! Don’t leave them standing in water cups, and try to dry them out while laying them out flat. Otherwise, the water will creep into the ferrule (the metal part that attaches the brush hair to the handle) and the hairs will eventually loosen. Good brushes can last you a lifetime if you take care of them! :)  

4. Try to paint a little everyday. You’ll eventually get to a point where you can feel whether there’s too little or too much water on your brush. You will also train your hand to keep it steady :)

5. Don’t throw away your paint when it dries out. One of the best things about watercolor is that there’s very little waste involved, and you can usually reactivate dried paint with a bit of water. I actually prefer this for smaller works, so I’ll only squeeze out fresh paint when I need a large wash on the paper. 

6. When rinsing your brush, wipe off as much paint as you can onto a napkin. This saves your water from getting muddy faster, and it’s just better for the environment! And then after rinsing, gently dab the brush on the napkin to soak up excess water. 

7. If you can, have two containers of water. One for mixing colors, and the other for when you want to lay down a pure color. 

8. Get a watercolor sketchbook to practice on. Sketchbooks can be handy for experimentation, swatch practice, and all that good stuff. :D 

9. Get paints with good lightfastness. Some colors are more prone to fading than others. Kind of like what I said in #2, it should say so on the label. Handprint has a lot of info on that if you’re curious. 

10. If you do want to clean your palette, dampen a tissue and rub away at the surface. It’s a lot easier than pouring water on the palette and then trying to sop it up with napkins. 

OKAY that was a lot, but I hope that helped!! That might have been more info than what you wanted to know, but let me know if anything was confusing. Best of luck painting!! :D