Successful Puppet Masters have 3 things in common:
Patience has to exercised when no one seems to be getting your clues. Clues are arguably the crux of the matter where ARGs are concerned. If nobody’s getting it you can have an NPC guide the player(s). That’s when a “neutral” [Out Of Game] place to put clues to be solved comes in handy.
Time management can be crucial to a successful ARG. If you have a plan to begin with use it. But don’t be a slave to it.
Imagination is a must. To have a successful ARG you should have an active imagination.