If you find that many of these tips seem to apply to a child at summer camp or school, that's because I'm getting most of my intel from my new job as an Inclusion Companion, a member of summer camp staff who works one-on-one with a child with disabilities to ensure they have a fun day. It can be rewarding, but just the other day I had a five-year-old throw scissors at my face, so it can really go either way.
1. Dump your ego
It doesn't work on them anyway. Just play their Sonic-vs-Eggman games where they chase you around the playground and you die a dramatic death bent over the mulch, and they'll respect you way more than if you were to scoff at their childish love for Sonic the Hedgehog.
2. Be uber patient
If you lose your shit, you lose your power (and also probably your job). If you need to excuse yourself to go take a breather in the child-sized bathroom down the hall, get another adult to take over.
3. Their tantrums
Building off of #2 -- During a tantrum, learn how to redirect a child's attention with fidget toys or questions about their interests or family. I've witnessed this in action and it blew me away.
4. Some choices
While there is a time and place for giving orders and expecting them to be obeyed, giving children a choice -- play outside or play inside, go to the bathroom or get a drink, go on the playground or play with a ball -- is more likely to get a response. Ask for eye contact and learn to bargain: five minutes of this for five minutes of that.
5. Their freedom
Let kids do creative things their way (as long as it's safe) even if it's ugly and wrong. This applies to arts & crafts, of course, not social interactions. Parenting may be different at home, but make sure to enforce the concept of boundaries and empathy whenever you can. Don't micromanage, though; sometimes, if you can get a kid to stay in the room, even if he won't participate in the activity, it's a win.
6. Use a system
Good points, bad points, rewards, bargains, instructions or a schedule written on index cards...different techniques work with different kids.
7. Don't take it personally!
The most important thing is to establish that you're in charge. It's not always your fault if a child won't listen to you; it's usually either a power play or the fault of parenting. Also, when kids act out it's not a betrayal, so don't treat it like one. Keep your calm and don't give them the cold shoulder as punishment (it doesn't work the same way it does on adults).
Lastly: Kids are balls of energy who learn by observing you, so set a good example whenever you can.