K.L.
When my son was that age, one thing that worked great was a poker chip game (he had a thing for poker chips...you can use marbles, coins, anything that your son likes). I created a chart that started with three or four discipline issues I wanted to address (brushing teeth when told, going to bed without whining, and a couple of others).
The basic rule went something like this...if he did what I asked him to do the first time, he earned one chip...I would give him one warning about the chip when he didn't respond immediately and if I had to repeat my instructions, he didn't get the chip...then, if he continued to resist or complain or whine or anything else, he owed me one chip if he eventually did what I asked (and two if I gave up fighting and had to use force...he got one warning about that too).
Then I set up a chart with the rules and a list of things he could "buy" with the chips (based on my estimate that he could earn 30 chips per week if he gave me "first-time-obedience" on every rule on the list). For example, he could trade 5 chips for an extra 30 minutes of video games, 10 chips to be allowed to stay up an extra hour on the weekend, 15 chips for an ice cream treat, 30 chips for a trip to the beach or Gattitown (I don't remember all the items but we had about ten...I asked him for ideas).
The first week was a bit rough...he earned some chips, but ended up having to give many of them back to me (including a couple of two-fers when he chose to fight). But once he realized I was serious about the first time obedience thing...that I wasn't going to give him second (and third and fourth) chances...that I wasn't going to count to three or anything else...he started enjoying the game. By the end of the second week, he was earning most of the available chips and losing very few for disobedience.
After a couple of months (once I was sure he had developed a positive habit), I replaced the original obedience issues with new ones and it worked on them too. We had to stop doing it about a year after we started because he learned how to manipulate it to his advantage...but it sure worked on him at three! (Note: his uncanny ability to get around the rules now at seven may have been enhanced by this game...but I think he got his ability to use rules to his advantage from me so...??? *smile*).