You want to check the expiration date of the strips, first. If they are expired, throw them out. And beware. If you are using something like red and blue litmus paper, red litmus paper will eventually turn blue and blue litmus will eventually turn red. So check the labels.
First, put the pH strips on something like a Petri dish or beaker cover, preferably on top of a white piece of paper. Then take a glass stirring rod ( alternate- plastic disposable pipette), put it in the solution to be tested, and then to lift a drop out of solution and put it on the pH paper. Then rinse the stirring rod with di water. This avoids contaminating the tested solution with the dye used in the test strips.
A word of warning. Ph test strips can be wrong. You can get oxidation occurring that will mask the pH.