As taught to me by my grandfather when I was a kid. Although he wasn't a Cockney, more a fan of word puzzles. This isn't rhyming slang. You've got to pick the letter each clue goes with. Say to your self... 'A' for ___, 'B' for ____, etc. I'll give you a couple of examples:
N for Lope (envelope) / B for My time (before my time)
(Some traditional ones are a bit difficult or old fashioned or rude, so I've tried to pick easier ones, though purists may not like them).
I think I've put the hardest / most unconvincing ones nearer the end.