Photo courtesy of Pixabay.com
A mnemonic is actually a memory device or technique which helps you remember information. For example...
'Many Volcanoes Erupt. Moldy Jam Sandwiches, Unusually Niffy, Phew!'
...is a mnemonic I learnt at school to help remember the order of the planets. The first letter of each word corresponds to the first letter of each of the planets, namely...
'Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto.'
As I'm sure everyone knows, Pluto is no longer a planet, but people were stupid back in those days and classed Pluto as a planet even though its obviously a dwarf planet!
|A rainbow, from red to violet.|
'Richard Of York Gained Battle In Vain.'
Once again the first letter of each word corresponds to the first letter of the colours of the rainbow in sequence...
"Red, Orange, Yellow, Green, Blue, Indigo, Violet."
If you wanted to use a mnemonic to remember the order of the alien comedy 'How To Save The World' books...
|The 'How To Save The World' books.|
Be Careful What You Wish For
By Whatever Means Necessary
Hopes And Dreams
Revenge And Justice
In The End, No-One Can Escape Justice
You might use something like...
'Awesome Brilliant Books! Hilarious! Read Immediately!'
'Average Bland Books. Halfway Run-of-the-mill Interpretation.'
'Abominable Brainless Books. Humdrum. Ridiculously Imperfect.'
But if you used the last one you'd be an idiot with rubbish taste. 
When he's not waffling on about mnemonics, Charles Fudgemuffin is also the author of the critically acclaimed 'Remember to put the bins out' note. Other less notable works include his alien comedy 'How To Save The World' books. The first book in the series is currently free for kindle from Amazon.*
* For UK and US readers only.