Slippery tiles- How can I make them slip proof?

You might try to method:

http://homeguides.sfgate.com/make-tile-slipfree-31912.html

How about using them on the walls instead? Or frame them as a group or individually and hang. Or make a serving tray out of them.

The acid etching will leave the tile more vulneraable to getting 'dirty' and is very 'iffy' as to how it will effect the tile's original ceramic integrity. It will also etch the grout that will becoe a dirt attractor, you wil have to reapply some protector to it. One solution might be to alternate them with a nonslip tile. But in general, I would not try and alter the manufactured surface.

Im dealing with this same issue in my living room of the house we just moved into. I've already fallen twice because the tiles are slick from the water being tracked in from all the rain outside. The solution I've come up with is to stencil the tiles! I went and purchased a normal latex based paint, but here's the trick... to help cut down on the slippery factor, I'm adding some play sand to the paint! It won't take much sand, just enough to make the paint a little gritty. Then just stencil on as usual. To make sure it all stays, get some clear poly add a little sand to that as well and paint over the stenciled tiles. This will seal the tiles and add even more grit. Now you have slip proof tiles! Good Luck and Have Fun!

not a good idea.