Choose a pair of reading glasses with proper strength and put them on. Get a magazine or a book to check whether you can see clearly through your reading glasses with that strength. Try more pairs including stronger and weaker than the first pair to see which one suit you best.
Go to any optical store to have an eye exam. The optometrist will prescribe a correct strength of reading eyeglasses for you. If you feel comfortable with your reading glasses on while reading and they provide clear vision for you, then you get the correct strength for your eyes.