If you're colouring something and you're not sure what colour you want to make it, put a clear sticky note over it (or some other clear sheeting) and colour that. If you don't like it, remove the sheet/note, put another in place, and try again until you find what you like.
If you're working on rice paper that you're worried the paint will leak through, lay it on top of watercolour paper or other similar substrate, and let the paint leak. Voila. Instant other paper with markings to work on for a future project.
When using acrylic ink or high flow acrylic paint on a gelatin plate, mix it with a little acrylic medium to prevent it from beading up on the plate. In fact, this will likely work for other water-based media that bead up on a gelatin plate, though I have not yet tried that.
Watercolour pans can be used for the portioning and storage of other rewettable media.
