Most concrete, unless newly poured, is not perfectly level. Over time concrete slabs crack, shift and settle. This results in a surface far from level. Apply a concrete leveling compound before you apply any flooring, including peel and stick tile, to a concrete floor. Follow the instructions; fill in any cracks, dips and level any humps until there is a level surface. Allow the compound to cure for the time recommended on the label before proceeding with further work.
If you install peel and stick tile on concrete, clean the concrete completely before you start installation. Verify that no dirt, rocks or dust are present on the floor. If dirt or rocks get under the tile, you run two risks. First, you might get lumps and bumps under your flooring, which makes it look and feel uneven. Second, if the adhesive sticks to a dusty floor, it is not adhering properly to the floor itself, which results in tiles that become loose or don't stick at all.
Do not apply the peel and stick tiles to a concrete floor without checking for moisture and alkalinity. Concrete often contains high levels of moisture or may be alkaline, which is unsuitable for tile floors. Either of these conditions might damage the tile or prevent it from adhering to the surface properly. These problems are especially common on new concrete floors that haven't cured for a year or two. Purchase the necessary testing kits from your home supply store to test for pH and moisture content of your concrete. Check the test results against the recommended thresholds on your particular tile product to decide whether installation on concrete is a good idea.
Prime a concrete floor before you apply peel and stick tiles. Primers for these tiles are made from a latex base. Talk to your flooring supplier about the appropriate primer for concrete. As long as all the other factors regarding concrete and tile are in favor of installation, just prime the floor according the manufacturer's instructions before you install the product.