2 year old tantrums

How do you calm your toddler down? My 2-year old son demands to get what he wants, when he wants, all the time. I guess that's the case to most toddlers but I'd say my boy's a bit different. If we say 'no' or if we ask him to wait, he'd throw things, cry aloud or lay down on the floor crying. We had him checked and he's completely healthy (no adhd or anything like that). Sometimes, I just feel so guilty as I also tend to lose my patience.