1. Use a sturdy surface. Hard surfaces are preferable over paper. Canvas and wood panels work well, as does some exceptionally heavy paper. If you are combing mediums, think of which surface will be best for both.
2. Use an adhesive that provides some protection for the paper materials (from chemicals, water, and UV light). Coat the paper on top and below. Add more when dry.
3. When in doubt, always test a small piece of your collage material before possible destroying a precious or expensive piece of paper.
4. Keep in mind adhesive can make things look darker and more transparent until it drys. It can change quite dramatically once it does, especially with the thinner and lighter papers.
5. Use a limited pallet. This will help your piece work better as a whole. This is easier than it initially seems because of limited printing inks.
6. Keep all reasonably sized paper scraps. They can be useful for later projects.
7. If you go paper shopping in person, take a snapshot on your phone of the project you are working on. It can help make buying decisions.
8. If you are combing painting or drawing with collage, have your composition figured out and figures and silhouettes correctly placed before beginning to add adhesive and glue. While you can collage over paint, its hard to fully removed the collage residue and go back to a pure painting surface.
9. Printed papers are not predictably sourced so you may not be able to find a beloved paper again at a later date. If you find something you like, stock up.
10. When purchasing on line, keep in mind the scale of the pattern displayed. Whether the repeating pattern is 2 or 8 inches across will make a huge difference in how it works with your project.
11. You never know what you will find or not, collage material wise. Work with your materials and allow for spontaneity when faced with the materials at hand.
12. You can always print your own collage material. I will be experimenting with this in the near future...