An important part of non-verbal reasoning tests can be the recognition and completion of patterns in a sequence of letters. This includes some eleven-plus tests and many IQ tests. By memorising the equivalent number for each letter of the alphabet you can solve these puzzles much faster.
My recommended approach is to first memorise the letters for 5, 10, 15, 20 and 25 then you can work from these and count onwards or backwards to reach any other letter.
I use the phrase Elephants Jump On Trampolines Yelling to remember these.
The easy test covers the numbers divisible by 5, the hard test covers everything else.