As Donkafelts say, there is really no optimal way. My personal default target values are:
VPIP 15
PFR 10
AF 3
But I do adjust to the dynamics of the table and how the other players are playing. For example on a loose/passive table my VPIP tends to go up or on a tight/passive table my PFR goes up.
The numbers I am aiming for is based on my personal experiences and my preferred style, but also on a fairly thorough analysis of players with the highest win rate at $1/2 level.