Hello, You DO NOT have to prep the tins for painting, as spray paint and acrylics work great. Have fun.
If you want to use something other than paints for metal or plastic, like regular acrylic craft paint, be sure and sand all surfaces well in several directions and dust off the residue so there will be a tooth for the paint. I would think it would be best to base coat the tin's sanded surface with a co-ordinating paint when decoupaging as well.
To keep tins from molting, sand and prep.
These little felt fish tuck away into an Altoids tin for a fun take with you game for the kids. This is a page about making an Altoids tin mini fishing game.
When giving a gift card as the gift, you can make it more personal and crafty, by making a cute box to contain it. This is a page about making an Altoids tin gift card box.