Here's a link to the tutorial on splitcoast:
Make sure you get the tumbled (unfinished) tiles from Home Depot, Lowes, Menards...wherever you get the color and price you like.
I printed my picture out on paper first, and then used a gluestick to adhere tissue paper to the paper (not glueing where the picture would print). Having the picture already on the paper gives you an idea of where to put your tissue paper on the computer paper. I know tissue paper's cheap, but then I only had to cover about 1/4 of the paper instead of the whole piece of paper.
Run the tissue paper covered sheet through your printer.
Trim the picture down to fit your coaster. You can cut through the paper and the tissue paper at the same time. Makes cutting a crisp line easier.
Cover your coaster in a thin layer of mod podge.
Place the tissue paper over it and spread another thin layer of mod podge over it.
Stamp a sentiment (if you wish) in stazon.
Add another layer of mod podge. Let dry.
I used 4 little furniture pads on the back side to keep it from scratching the furniture (the kind you put under your dining room chairs to keep the chair from scratching the floor). You can also use cork instead.
These make a great gift for grandparents.
You can also do this on bigger tiles and prop up in a plate stand for decoration.
Feel free to PM me if any of this isn't clear!