Given IQ like many other human traits can be modeled as GxE, one can optimize the "E" part, which boils down to avoiding ruining the realization of genetic potential of the child (i.e. the influence of the environment is often negative). There is a list of small factors in early life that are associated with IQ and related life outcomes. Mostly these tend to have something to do with pre-natal, natal, and early childhood environments.
To give just one innocent example - the month of conception statistically influences many life outcomes, including lifespan (+ 6 months of it if the child is conceived in winter and born in autumn), likelihood of Alzheimer's, multiple sclerosis, and 2-4 points of IQ difference.
One can argue here about statistical controls, but let's avoid this line of thinking.
> If you have questions regarding IQ and how not to ruin it, mail me
Well, would you mind giving us all a hint here? I'm curious.