You have created your resin pieces and pushed them out of the molds, but they are rough around the edges...literally! I have outlined below a great way to sand down your pieces to the smoothness you desire. Pics above help too!
1.) Buy a pack of mixed grit waterproof sandpaper. (You can get these at any home depot or the like)
2.) These packs have assorted grits from 220 (very fine) to 600 (ultra fine). This is the type of paper that you can use in water. Why would you want to use the sandpaper in water you ask? Using a shallow pan of water like the one above helps keep the tiny resin dust from getting in the air and into your lungs.
3.) I found that if you cut a small piece of the sandpaper and wrap it around a nail file you can maneuver it with great ease, then when you are done you can dispose of the used sand paper grit. Cutting the paper down will help you to save the areas that go unused for your next project. I have had the same pack for a while now.
4.) Try different grits and see which one give you the outcome you want. I use the 220 because I like to sand down the sides pretty good.