First of all, you need to decide what type of bed mats you want to mount on the tailgate of your pickup truck because there are a huge variety of bed mats for tailgate.
You should select only those tailgate bed mats which are made of rubber because these mats are long lasting and also are good in protecting the surface of your tailgate.
Take measurement of the tailgate of your pickup truck before purchasing the tailgate bed mats. It will give you a better idea of the size of tailgate bed mat required for your pickup truck.
Now, open the tailgate of your pickup truck by using its handle and place the bed mat by keeping the tailgate in a balanced position.
Make sure you have placed the bed mat in the middle of the tailgate otherwise you will not be able to cover it fully. You can use a measurement tape in order to verify whether you have placed the bed mat into the middle of tailgate or not.
After that, find the screw holes in perimeter and drill self tapping screws on all four corners of the bed mat.
Try to open and shut the tailgate of your pickup truck in order to make sure that tailgate is working properly after mounting the bed mats on it. If there is any problem in the movement of tailgate then adjust the bed mats accordingly.
Now, you should again open the tailgate and install the remaining self tapping screws by the help of a drill and then shut the tailgate after completing it.