There are four distinct ways of memorizing. Each person falls into one or more of these categories. Some people have better visual memory, i.e., the more they see something, read it, the better they remember it. Some people have a better aural memory, i.e., the more they hear it, the better they remember it. And, some people have better tactile memory, i.e., touching or feeling, for example musicians, what needs memorizing works best. Last, some people memorize things in relationship to other things, looking for connections between the items that they need to memorize.
And, of course, many people use a combination of two or more of the above.
So, the key to memorizing is figuring out how you learn best: ears, eyes, touch, relating or a combination of these.
You may be using the wrong method for you. So try one or a combination of methods listed above to find out what works for you.
Good luck!