Ahh, yes. My son is 18-mos old and heading towards the terrible two's at full-tilt boogie! This is my advice, and it works very well for MY child. I am a firm believer in discipline. My child needs to know that there are quick consequences for his actions, and when the need calls, a spanking. I give him until the count of 3 (and 99% of the time he's over it by 2) to stop whatever bad behavior he's exhibiting. If he continues, then it's an open-handed swat on the butt. You would be amazed how quickly that works. I don't hit him for any old reason, it has to be deserved. I get down on his level, hold his arms with my hands, and speak in a low, firm voice. After the counting or the spanking, he usually turns around and gives me a hug and a kiss. Everyone has commented on how well my child behaves, and that is because normally all it takes is a warning for him to straighten up. Kids need to realize they are doing something wrong in order for them to behave correctly the next time they get angry or frustrated. I believe in a mix of both positive and negative reinforcement. I praise my child constantly for good behavior and affection (he's a very affectionate child - lots of hugging and kissing - mainly because we hug and kiss him constantly). We tell him that we love him a million times a day. Every kid needs a balance - trust me, if they learn early on that they can railroad you or take advantage (especially in a public place) you'll never be able to gain control at times when you'll need it most.
I know this is long, I'm just trying to explain what works best for my family, I hope this helps with yours!
Best Wishes,
Meg