Good for you for recognising you could find some pointers helpful. I think a lot of this starts with your attitude. If you approach things with an expectation that they will mind what you say, because they know you are in charge, a certain authority comes with that.
To me, what really helps is to be clear with yourself that you are in charge and for good reason. And it is for their benefit that you are. Small children do not have the life experience or intellect to safely or beneficially run the show - eg if you tell your child that cars are dangerous, it's a bloody good job that they believe you and listen when you tell them not to run out into the road. It's also good for them to understand there are certain expectations around behaviour in different settings, how they should treat others etc. If you're very passive with your child, how will that go once they're in their early teens and not used to listening to you? It might help to see it as a kindness to them to get on top of this now.
It helps to have clear boundaries and consequences for not doing what you ask. As others have said, don't make it optional in the way you tell them what you want them to do and be clear in the way you communicate: 'time to get your shoes on, we're leaving in a minute'. 'Get down from that wall', 'give the toy back to Olivia, she was playing with it first, don't snatch please'.
Countdowns to transitions work well, so they have time to accept what's happening and are not abruptly expected to move away from things: 'ten more pushes, then it's time to come off the swing and let someone else have a turn' - then count the ten pushes, and then get them off.
If they don't comply, you can do a count to three, before issuing a consequence that you've warned them about, For some children, though, this kind of trains them to always wait until you're about to say three before they do what you ask, so watch out for that. If they start to push boundaries, going to an immediate consequence without warning can act as a reset. I've found I only ever need to do that once or twice and only when it was something very important (like a safety issue).
Implementing this generally will stand you in good stead when it comes to times they might not otherwise be bothered by a consequence - like getting in the car seat - because they're already in the habit of doing what you ask, by and large.
It can be hard at times! Especially if they push back or get upset. If you don't like upsetting your child, which is understandable, I find it helps to take a longer view - it's better for them to be upset a little now, than to experience a greater upset or harm down the line. And don't forget that young children are moved to tears very easily, over not very much, often, but they quickly get over it and move on.
I think it's good to balance this sort of approach for the things that matter with giving them choices and autonomy where possible, so they feel they have agency and an age-appropriate level of freedom and autonomy.
ND children may well need a different approach, of course.