We been going thru it lately with 5 year old and realized we dropped the ball on a few things. Been reading up on some things after we realized we started to repeat some of the mistakes our parents made.
A couple of things that we've found success with over this last calendar year:
1. Use clear, concise language. At this age, he understands feelings so we try to always attach how each action makes us feel.
2. Establish the Top 3 rules (really principles) for them to live by at all times, put them on a poster and put it on a wall where it's visible at all times. I sat down and let him help design it (he picked the colors of the markers while I wrote down our 3 rules). Tailor it to the needs of your child but once you agree to them, stick to it. We read the rules first thing in the morning and before going to bed at night. Refer to them early and often (Why are you doing that? What's the second rule? ).
3. I created a sticker reward chart. He earns a sticker for doing the right thing (following the rules without being prompted or reminded, good report from school, being helpful, anything positive) and loses one for doing the wrong thing (breaking the rules, forcing us to repeat a directive, being a dikk). If he hits our goal (5 stickers) at the end of the day, he earns a small reward (extra playtime/snack/etc). If he earns 25 by the end of the week, he gets a surprise (play date, outing, screen time). Be consistent with the rewards and consequences and don't get odee with the prizes. The focus is reinforcing the right behavior while teaching that unacceptable behavior is met with swift, natural consequences.
4. Don't get into the tug-of-war power struggle. Drop the rope.
5. Be present. We're all guilty of just wanting to unwind and turn off for a few, especially after a long day. It's easy to turn on a tv or hand them a screen so you can just scroll or whatever. It will come back and bite you eventually. Your child needs the original face time and not just you sitting next to them with your face buried in your phone while they do something you are barely paying attention to. I've been really working on this one over the last month and I've seen a difference in his temperament. In the evenings, we play, read and do some other activity (painting, coloring, board games) together as a family. The more time we spend doing things, the less frequent the tantrums and requests for screen time.
*bonus* eliminate screen time during the work week. Seriously. Limit 1-2 hours per day on the weekends.
I'm guilty of that. 
I might start incorporating this. We moved away from "don't be bad" to "we know you're good" but I like "right" vs "wrong" better. Good looks.
