I agree with making sure it's stipped. Assuming you actually have sheet vinyl (made of actual vinyl) instead of linoleum (pressed paper product w/linseed oil) this is the steps you can take to ensure you're job will last as long as possible. The best thing is to strip the floor using something like Armstrong's NEW BEGINNINGS. It'll get rid of any residue from previous cleanings. Next, if the floor has a raised pattern, you'll need to use a leveling embosser to smooth over the patter. Reason for doing this is because any pattern on your previous floor will eventually transfer through onto your new floor. Then you'll need to use a latex primer for self stick tiles. Armstrong recommends this so that the tile will have maximum grab and less lifting. Find your center with a chalkline, as someone else here said. Now it should look like a giant cross having the intersecting lines being your center start point. Now, you'll have to make sure that the angles made are a perfect square, otherwise you'll be out of measure by the time you get to the otherside of the room. Use the 3,4,5 rule. From the very center measure 3 ft up, mark, then 4 feet horizontally, mark. Now measure from the first point to the second. If you get 5 ft, then you're starting corner is square and you may begin laying your tile. Dry lay some tile to make sure you've got a good patter. Don't forget to lay them all in the same direction as per the arrows on the back. Now if you're happy at how it'll look, lay your first tile lining up both edges again the chalk line you've made in the center. Then lay one to the right, and the other on top so it looks like an L. Continue to lay them in a piramid style to ensure you've not defiated from your measurements. Do 1 quadrant at a time, always starting from center. Have fun and hope this helps. ALWAYS FOLLOW MANUFACTURE INSTRUCTIONS SO THAT YOU DON'T VOID ANY WARRANTE.