Hmm tips.
Obviously choose your battles, what is really important, and is it important? If it's not really that big a deal then it's better to just leave it.
Choose your consequences suitably, the 'punishment' must fit the 'crime', like the toys don't get picked up by the child, they get picked up by mummy but put elsewhere, be it bin or a 'removed toys box'.
Always think about why they are acting the way they are, e.g DP got annoyed with DS the otehr day for bugging him about something, the reason behind it was DS is 3, time to him is a totally different concept, so Daddy saying give me five minutes, that's fine, but two minutes later he will ask again because he has no concept, so try to take away that issue, use a timer if it's a time issue.
Another why question, Is it the time of day, eg if I put the DC's in the bath when their fave tv programme was in I'd be less lkely to get co-operation, can you reschedule things so they suit them?
Speak to them calm, collected and neutral when asking to do something, then if you need to use your 'not impressed mummy voice' you can use it as a sign that things arent going well and it neednt descend into shouting or arguing.
Give reasons and respect. 'Don't speak to mummy like that, it's rude, I wouldn't talk to you like that, if you want to talk we'll talk, but talk nicely' works wonders on my two, also, if they tantrum/cry/yell etc, ignore it, tell them you cant talk to them in that state and when they have calmed down you will be happy to discuss the issue, then walk away.
I'm sure there are tons more, and I bet I've x-posted loads but they are my tips that I try to live by.