Personally I don't like the idea of using rewards and punishments to motivate kids because it sends them the message that whatever you were asking them to do must be unpleasant or you wouldn't need to bribe them to do it. Telling kids they can't have dessert unless they finish their peas reinforces the idea that peas are not tasty. Instead you could give them the option of eating peas when you are and not pressure them about it in the hope that by not privileging one food over another they will come to enjoy a variety of foods on their own. With things like chores around the house I would like them to participate in those as they get older simply because they are part of the household and these things need doing, not because I said they have to do them or bribed them to.
As for punishments, I really don't like the idea of spanking since you can't just hit anybody else (friends, coworkers, partners) who isn't doing what you want and I don't see why kids should be the exception. I don't much like time outs either because they seem to upset kids without really changing their behaviour.
Instead of threatening I try to offer my kids (well, my eldest, the toddler is too young to get it) choices and explain what the consequences of her choices will be, eg. "Throwing your toys like that is dangerous you could hurt someone. You can either play gently with them or we can go out for a walk."
That's the theory, but I still relatively new to this parenting gig so I will have to see how it actually pans out over time.