For us, if it is something non negotiable, then either DS1/DD does it themselves, of I will do it after a certain period (if there is a time limit, like brushing teeth before bed, I give them a 10 min grace period, then I do it how I want to do it, usually with the tooth paste they don't like, with the tooth brush they don't want to use). If there is no time limit to it (putting shoes on to come outside to play can be an issue here- they need to wear shoes because we have serious bindis, and the ground gets really hot) then if they haven't done it themselves by the time the other two children have done it, we go outside without the child protesting, until they put their shoes on (so their feet are safe, and not injured).
Generally though, if they won't do something like feeding themselves I just refuse to do it for them. They are clearly not hungry if they won't feed themselves. They get a time period and if the task is not done (eating/dressing/packing up) they face the consequence- no dessert (if we have it, or fruit if we're not having special dessert), they go out in their pj's if they're not dressed, the toys they leave on the floor gets donated to a child who will treat their things with respect.
Try to have consequences which are unpleasant for the child, but relevant to the task. And something that will help teach them why you need tasks done.
I need you to pack up your toys so that our house is tidy, and therefor safe (no tripping hazards), and so your toys don't get ruined if we walk on them. If you can't look after our house and your toys like that, then I will donate them to someone who would like your toys and who will look after them.
I need you to get dressed because your pj's are at home clothes. But if you really want to, you can schlep around the shops in them/go to pre school in them. Your friends might think it's a bit funny that you're still wearing your pj's though, because they're bed time clothes.
Etc....At 4 he should understand such actions and consequences. Hope that all makes sense!