Sparticus has described pretty much how I use Acrylics. To me they are God’s gift to artists,quick drying,opaque or transparent, you just keep going till it all looks right. It means that the start of a piece can be disheartening but once you get a good skin over the canvas things become easier and the later stages can feel almost like drawing in colour, you get used to fading the edges of layers or dry brushing as a means of blending .