The difficulty with memorizing multiplication facts is basically one of storing a large amount of precise (3x4=12 and not 11 or 13) information and retrieving it very quickly. But storing them haphazardly means you won't know where to look for them when you need to.
When my son had great difficulty memorizing them, I developed a method where I first reduced the number of facts to memorize to a minimum; for example, did you know there are only 3 facts to memorize in the 7 times table, 2 facts in the 8 times table? Then I provided him a visual map of each table that he could store in memory in an organized fashion, so that retrieval is as easy as checking the internal map for that table and seeing the answer. The method works as well with gifted kids and adults as it does with those who have dyslexia or other learning difficulties. I published the method in See and Learn Multiplication By Heart (ISBN 9780973320916). Sold on Amazon, check it out, you will never need another method. Everyone can learn their facts by heart easily without stress and endless practice.