The thing I hate most about painting. The best thing to do, as mentioned earlier, is water down the paint a bit, maybe 3 or 4 drops of water, and when you dip your brush in the paint wipe off the excess moisture on a paper towel. Matte medium also helps. I use vallejo matte medium when I paint metallics and colored areas, sometime not always, and it really helps with tide marks. Again the mixture should be diluted with water.