This list subject to random updating when something hits me. The management thanks you for your perusal.

• 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.
  
  
• You can make bookmarks/tabs for cheap by attaching ribbon to paper clips.
  
  
• Instead of using water to thin out your acrylic paint, try using airbrush medium. Particularly in underpainting, and particularly with cheaper brands or student lines of acrylics, too much water can break down the bindability of the paint to the substrate, and eventually lead to the painting literally cracking or peeling off the substrate. Using a high flow medium, like airbrush medium, gives you the liquid consistency you're looking for without breaking the bindability of the paint.
  
  
• A simple way to clean off a surface covered in acrylic paint bits is to cover that surface in a thin layer of gel medium (or acrylic paint), lay paper over it, press the paper down in the same manner you'd do if doing a hand print, and leave the paper there until everything is dry. Pull up. Voila. Clean, or mostly so, surface. You may need to repeat this process more than once. This also works for cleaning gel plates (commercial, et al). The upshot is that you now have a metric fucktonne of collage paper, or substrates for future artworks.
  
  
• In order to help prevent your watercolour paper from buckling, you should use at least a 140 lb cotton rag or better. But the main thing, no matter the paper, is to wet it on both sides. This doesn't tend to work so well with 90 lb papers because they just can't take the water load. So, if I do happen to find myself possessed of 90 lb papers, I save them for really light things, or printmaking of super thin layers.
  
  
• 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.
  
  
• If you're using a gel plate of some kind or other, either commercial or homemade, and you want a sturdy surface to put it on that can also afford you the ability to trace from other sources onto the plate, then you could put your gel plate on either a piece of Plexiglass/Perspex, or a glass cutting board, both of which can double as a permanent bed for the plate, so long as you have a good way of covering it to keep the dust off when it's not in use.
  
  
• 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.