I tried making miniature decals for the first time already some time last year. I made just few ones to start with and they came out fine. Here are two plates which I decorated with them then.
Now I wanted to make some more and I decided to make a whole sheet of them at a time. After printing the pictures on the paper (inkjet waterslide decal paper) I let the ink dry for half an hour before spraying the sheet with varnish a couple of times. Now I will just have to be patient enough to wait until the varnish has dried - that is the most difficult part! :-)