I tried that as well and it does not work for me. What works is association with some stories. For example, to remember a credit card number I associate each 2 digits with a year that gives an event and then the number is a sequence of events.

What also works for me to train memory is to learn phrases in a foreign language that I do not understand. Surprisingly combining those with text I do understand leads to better recall of the whole text. It is almost as understanding harms memory.