Sometimes it is the small things that makes painting session go more easily.  Here are a few notes from my easel:

• If your palette colors have dried out, put a drop of honey or glycerin on the pan and let it sit.  The honey or glycerin will attract moisture from the air and hydrate your paints.   If they are REALLY dried out (petrified) give it up.  Scrape the paints out and start fresh.
•    I prefer to let my palette dry out between uses because it avoids mold growth.  The one time I did put a wet sponge on the palette and covered it with wrap, I found a disgusting blue fuzz on the paints the next morning!
• I avoid using a hair dryer to speed drying since it dries the paper from the outside in instead of the inside out and even when the outside is cooked the inside is likely still damp.  I prefer to take my time and let a painting dry naturally (usually overnight) before putting another layer on the next day.    It is possible to add a few drops of alcohol to speed drying but the paints will settle differently.
• If you want paint to dry more slowly, mix a bit of ox gall or flow medium with the water.  You can also prime paper with it.
• If you are working on a large painting you may want to mix your colors in larger containers to avoid having to stop and mix colors. I use ceramic muffin pans (for microwave use) or ceramic divided plates for the purpose.  Those are nice because you can get a wide brush full of paint.
• Keep a piece of scrap watercolor paper near to test colors.  If you make notes on that paper you can punch holes and keep the color notes in a looseleaf notebook for later study.
• Test for paint dryness with back of hand.  If the surface is cool, it is still damp and it is better to wait a while before adding another layer.
• Prevent harsh edges between light and dark. Dampen the paper on both areas and lay down light tones and allow paint to flow in areas to be covered with darker
• Don’t press down when painting washes or you’ll get streaks and be careful not to put pressure on the paper with the side of your hand.
• Turn paper around and upside down when working to help the paint flow where you want it to.