My Watercolour tip of the week is to just let it flow. When you want a smooth, seamless expanse of paint, as in a peaceful sky, one of the ways I like to use to get that effect is the Wet-In-Wet technique. First, you need to decide where you want the colour to go, and then get the paper in that area quite wet. Then make a puddle of the colour you want to use (see, I said this was playing in puddles!). Charge your brush -make sure it is one that holds a lot of colour, and drop the wet colour onto the wet paper. Do this several times until you have fluid puddles of colour across the paper, then put you brush down and gently start moving your paper around to make the colour puddles flow. Eventually, the colour will flow across the whole of the wet area. You will likely still have puddles of colour gathering in places, so the last step (if doing a sky) is to turn the paper upside down and let the excess colour flow to the bottom. It helps give you the lighter horizon line you may want, and when the colour pools along the bottom of the paper, you can wick it away with a large brush, leaving a smooth, unbroken sky. If you want to add some interest to the expanse, wait until the surface looks shiny, but not soaked, and gently blot some colour away with tissue. This technique can used in areas other than skies, you just have to be a bit careful to not let the puddles overflow onto areas where you don't want them.
So get your puddles ready and start having some fun!