There are twelve favours in total, three in Cuba, three in New York and six in Florida. To find each one, you can either search the map for a symbol of a little man, or go to Don's View then go to corrupt officials. Once you have found the favour, you are looking for go and find them, speak to the official and get the favour. Once you've done this, you do the favour and earn a favour from them. To check which ones you've done instead of clicking on corrupt officials go to collectables and see which favours your missing. This achievement is reported to be glitched for some people so to be on the safe side save your favours until you've done all twelve. If it does glitch on you, then redo all of the favours and if it still doesn't unlock then you will have to restart the game and do them all over again.