My advice:
1) stay calm-don't yell!
2) stay kind
3) be very, very specific. In fact, for our now lovely dd23 (who is also PG), we wrote nearly everything down. We had contracts for everything and we used lists. We had (and still have with our children at home) family meetings weekly, and we took copious notes when dd was little (she'd often argue the specifics of what we asked, what she was supposed to do, etc).
4) don't argue - see above. My God, when they're PG, they can argue ALL DAY. I'm not saying to not give them an explanation if asked, but that's it. I don't negotiate all day, especially on stupid stuff (and yes, I actually do get to decide what is stupid stuff).
5) Don't put up with disrespect. If I got an eye roll as she was leaving the room, I let it go. If I got straight on making faces/rolling eyes/yelling... I just calmly said, "I'm not going to have this conversation with you if you can't ask respectfully." Then I'd leave.
6) position them to be successful. Don't let them make bad decisions to "learn a lesson." We don't put sweets in younger ds's lunch because he can't remember to eat healthier food first. We had a TV timer for years which shut off automatically after the kids reached their daily limit, so they didn't have to remember. Don't rely on willpower.

We didn't do a lot of punishments, to be honest. But we were pretty strict. I think that by making sure they made good decisions (sleeping, eating, planning homework, etc), we had fewer conflict. But, in the end, parenting really wasn't a democracy for us. I don't yell at or hit my dh or my kids, but I do tell my kids when to go to bed (at least at 6) and I let my dh decide for himself.
I also think SO much depends on the individual kid. We have one grown child with whom I've rarely if ever had a conflict. we have another who is that rare teenage boy who will come down to the kitchen at 6am and unload the dishwasher, start my coffee, and make his brother's lunch. Then... we also have our oldest, who routinely had little self control, argued a ton, and was overwhelmed by her emotions rather frequently. And we have our youngest, who although not as emotional, will often make bad decisions due to lack of self control. So, he logically knows that he should (do his homework/put his stuff away/go to bed etc) but he would have lacked the self control not to watch ESPN all night if we hadn't stepped in. Yes, some kids would catch on after being exhausted at school the next day, but believe me, not all. I think at 6, you want to limit the explanations and negotiations and conversations. Treat him well, treat him kindly, be specific, but be the parent. I don't think that what you need to do is very different for a PG kid, but you might be more likely to end up frustrated and exhausted. ;)(and btw, dd23 is now a wonderful, respectful, and kind daughter and sister... and youngest ds, now 11, actually turned OFF his favorite college bball team this weekend to do homework... enough guiding and helping and they eventually do catch on).
Good luck.