Awesome!! I've been meaning to do that for so long now. I'm pretty good at crafty stuff so hopefully when I find the time it'll come out as nice as yours! Do share your technique if possible, a few pointers would be greatly appreciated!
I have a tool that has a sticky rubber end and the other end is a very thin point.
I have a newspaper spread out to catch any crystal and so I don't get glue everywhere on top the paper I put a black piece of cardborad again to help with lost crystals the black makes them really easy to spot.
I put a blob of craft glue on the black card and pick up a little using the pointy end of tool spread over a small area of the item (in a line rather than a sqaure) then using the rubber end pick up your crystal possition on the glue and use you pointy end to push into place.
Only apply a small amount of glue maybe enough for 5 crystals before you need to add more, whatever you feel happy woking with basically, oh and make sure the glue you get dries clear
The way I positioned the crystals was (with the gaps between lines)
000000
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so basically first row all crystals side by side next row the crystals move along very slightly into the gap between the two crystals above (like when you look at a brick wall)
I'd play around with it on you card first to see what look you like best, also have a look at the website that do it to see there gallery maybe your phone is there and there's a better way of doing it.
I'll try and take some step by step pics of the next thing I do to help
but I'll answer as many questions as I can