27. Storing the wonderful art you receive may be a concern. I have most of my mail art in 4"-deep 3-ring binders. Protective plastic pages can be purchased in different designs, like full-sheet, 2-pockets-per-page, 4-pockets-per-page (photo storage sheets) or 9-pockets-per-page (trading cards) available through eBay and other sites. The decorative video tape (photo) storage boxes are also useful. To display some favorites, you could use hanging jewelry holders with clear plastic pockets (like shoe or purse organizers).
26. To help collage elements stay securely attached during postal processing, first glue (search out glue options), then press between waxed paper in a thick book, and weight down with a heavy object like 1 gallon jug of water, overnight until dry.
25. Easy abstract backgrounds for art can be made with acrylic paints dropped on shiny-side-up freezer paper. Just spritz with a little water, then place your post card or Artist's Trading Card on the diluted paint, move the paper around, and then admire the smooshed design. This may be repeated with the same color for more intensity, or with different colors after each application dries.
24. If you want to use a magazine image or other image that's not quite the right color or needs background color, scuff or blot lightly with an inkpad of the preferred color. The small oval "Cat's Eye" ink pads work well for this.
23. To alter Rolodex cards that seem thin and flimsy, securely glue two of them together.