First of first is the first of you second of you is the double of you first of last is the last of you Tell me who are you?

The riddle is describing a sequence where the first letter of the Word "first" is 'f', the second letter of the Word "you" is 'o', the double of 'f' is 'ff' (the second letter of "off"), the first letter of the Word "last" is 'l', and the last letter of "you" is 'u'. Putting it all together, the answer is "follow."