Mnemonic techniques are very useful. In case of numbers (dates), you can use an old technique where you assign consonants to numbers:
0 = s
1 = t or d
2 = n
3 = m
4 = r
5 = l
6 = sh or ch
7 = k or g
8 = f or v
9 = p or b
Then you take two numbers and fill in random vocals to get proper words.
For example, in case of the french revolution (1789–1799), you can create "dog", "fabio", "dig", "pope". Then you take an area that you are familiar with, your home for example, and you assign the different dates to different rooms, preferably in a familiar sequence, like entering your home and going through all the rooms in specific order to get to the one furthest from the door. Then, say, the first room is your living room, and then you visualize in your living room a dog hanging from Fabio's hair while he is digging a hole for the Pope's body, while there's a French revolutionary standing a few paces away with a smoking gun.
It sounds difficult, but it's very useful for memorizing large quantities of numbers with no error.