I put about a tablespoon out every 2 days. If there's any left in the bowl I empty it. They hoard most of it anyway
I give veg every day - some people say every other day. Just a teeny tiny piece though, thumbnail sized, and rotate between broccoli, carrot, cucumber, cauliflower so he has something different every day. Variety is the spice of life
Charlie gets half a nut once a week as well - half a brazil nut or pecan usually. Plus a Monkey nut once a week. The veg always gets eaten straight away. About once a week he'll get a tiny piece of apple or banana as well. You can also supplement with the odd piece of plain cooked chicken or beef too.
So each day he has his hamster mix in his bowl, his veg somewhere else, so he has to get off his backside and go and get it (I put it in his sputnik). And something extra - either a nut, or a small piece of cheese or fruit, or a healthy hamster treat, also put somewhere else so he has to go and get it
Usually on his kabob which is at the other side of the cage.
The good thing about the veg each day is - I know he's been out when it's gone in the morning. I'd be worried if it wasn't.