Most tile and flooring products come with instructions for their installation. These instructions detail all the steps you should take, including preparing your surface. In most cases, you should remove the existing flooring. However, you can tile over existing tiling if it's in good condition. You should always clean your surface before laying new tile or flooring down. Trapping dirt, dust, and debris underneath your new floor may impact your finished job. Use a broom or vacuum to clean your surface before laying your tile or flooring down.
Traditional tiles need underlayment, which creates a waterproof barrier between the tiles and the subfloor. Laminate flooring also relies on underlayment for support. Without it, your floorboards could crack or separate at the seams.