What we did:
First we painted a "grout" color I chose an off white
Then when it dried we measured and marked for the tape. We measured the height from the cabinet to the counter and then halved it. That is about where you want the "tile" points to meet.
Then the instructions I found said to use the measurement you took as half the height and mark along the top under your cabinets. (This didn't work out perfectly for us so we had to kind of eyeball some of it) Do the same across the bottom. Your tape will go from the first top mark to the second bottom mark (skipping one). We taped all the diagonals in one directions then went back and did the opposite. The ends will have a shorter piece of tape that goes from the second top mark to the middle point (height wise).
Just to break it down for you:
Our height from counter to cabinet was 1ft. So we marked across the top and bottom every 6". Our lines intersected at 3", 6", and 9". This happened naturally if you tape like I said above. Some of our lines got off so the tape didn't always land right on the mark but if you eyeball it it will come out looking good.
The hardest part is the taping...DH works in building construction so he's good with measuring and numbers. To paint I used a light tan base coat and used a sea sponge with lighter and darker colors to create texture. You have to be real careful not to get a sponge paint look; I put two colors on at once. I used an eggshell finish and faux rock switch plates to make it look more like tile.
This is hard to explain in type so please feel free to e-mail me if you have any questions: firstname.lastname@example.org