A wizard

A small dog

Aside from medicine and whatnot:

Make it so that reproduction is somewhat easier / less painful

Make people on average taller / make the usual range of heights less extreme (like, make it so the average man is 6' tall instead of 5'4", and make it so there's a similar range in height among women)

Make people generally faster and stronger (with the tradeoff being that they'll have less endurance and won't be able to sleep as much)

…and then I guess beyond that I could see modifying some traits that have been selected for in different human populations (e.g. lactose tolerance), but I'd be wary of having too many "different breeds" that aren't very closely related genetically. I'm not sure I'd want that many real-world consequences in a "toy world." (Admittedly I am not well-educated in human evolutionary genetics, so this may not make sense)

I guess I would want to make humans better at living in cities, since they are now so dependent on them.

I don't think I'd want them to live longer (beyond whatever technology allows), because I think human life has a natural upper bound and we're already stressing the planet to the limit. That's probably controversial, but I feel like it's a consequence of the previous point. I feel like there are good reasons for thinking that civilization will fail to some degree in the next century or two, because it relies on several fragile things, so I'm not sure I want to include "extend the human lifespan as long as possible" among my interventions.

Идет медведь по лесу, видит, машина горит. Сел в нее и сгорел.

!

1. Take care of yourself

2. Do something you like to do