Ways to improve Intelligence?

The malleability of Intelligence is factually proven. I have written about short-term and long-term changes (due to pharmacological factors and environmental changes).

Now I’m looking for more influences to boost Intelligence – I took a look into Intelligence / Cognitive training, though it’s being heavily critisized, hence I’d rather go with something else. Does anyone have articles / any ideas on which other methods, categories and so forth might improve Intelligence?

Vague ideas I had in mind are psychological and behavioral influence.