If you don't think VAR is going to eradicate referee mistakes, I'm not sure what you mean by implementing it so that it is effective.
I'd address one or two aspects of the game first, before applying it unconditionally.
Firstly, offside decisions: instruct all linesmen to let marginal calls proceed and they have the ability to ask for a review when play next breaks. I would let all marginal goals stand unless a player is clearly offside on VAR.
Secondly, sending off offences. Referee makes a decision one way or the other, and has the ability to ask the VAR official if they can see any obvious reason why the on field decision should be overturned.
These two aspects alone with throw up confusion. People will ask what offside is - is it determined by feet position? Who is deemed interfering with play? That sort of thing. Let's iron out those wrinkles before trying to fix the whole sport with television. Apart from anything else, people might actually bother to learn the rules because you do hear a lot of crap surrounding contentious decisions at the moment - even from pundits who have played the game for 20 years and should know better.