The first behavior I can think about is taking antibiotic. I think it is not a good behavior because antibiotic might kill good and bad gut microbiome at the same time.
Second behavior is consuming more fiber in diet. Fiber in the diet can help to clean the waste in the gut as it is not soluble in water. It can help to create a better gut inner environment. Also, fiber can promote the growth of probiotics, as it is the food of probiotics.
Third behavior is breast feeding, which is related with babies’ gut health. Breast feeding is encouraged since mothers can transfer beneficial microbes to their babies through their milk. It could help babies to set up their gut environment more quickly.