Choose a position for your towel rail. Measure the distance between the fixings on the base of the towel rail and transfer these measurements onto the wall. Measure an equal distance down from the bottom of a tile and mark the measurements to make sure they're even and level.
Remove the tape and insert the wall plugs into your holes. If you need to, use a hammer to gently tap the plugs in.
Using your drill, screw the plates into the wall plugs so that they're flush with the tiles.
With your tape measure, check that the distance from the plates to the edge of the tiles below them is the same. If not, then you'll need to make adjustments. This will ensure your towel rail will look straight once it's installed.