Wow, I feel like I JUST went through this...because I did. The first thing we did (throwing) was to tell him that we don't throw X. I would then hand him something that he can throw, and explain to him that balls, etc. are for throwing but X isn't, it is for Y. If he threw it again, we would tell him, he would lose it for 5 minutes (and set the timer). If he continued to throw it, he might lose it for this entire wake time, or the day.
Hitting is the worst. I tried the holding hands thing, and I could feel him tensing up. The moment I let go, he would hit again and be frustrated on top of it. We had already been through the "soft touches" earlier with our cats. If you haven't taught him soft touches, then now is the time. I would take my son to the ottoman and ask him to show me soft touches, and hits. I told him that he could hit the ottoman, but not people or animals because it hurts to hit and gives boo-boos. People need soft touches.
In the last few months (he is almost 22 months), we started with mommy getting a time out when he hit. He seems to only hit me and he is very mommy-centric, so it seems to work for us. I started with, "If you hit mommy again (holding the arm that tried to hit), she will have to go to time out." I then let go of his arm, and if he hits, I say, "You're done", set him down and walk away. I usually sit across the room where I can still see him if I am home alone with him, or wherever if my husband is there to step in. My husband will usually then talk to him about why I am in time out.
He says the saddest, "Mommy", and cries. The first few times he tried to get my attention, I would tell him, "No, mommy is in time out because you hit her, and hitting hurts." I would ask him if he understood, and if he wanted me out of time out, he always said yes, and I had him say please. I would ask for a hug, and after a quick talk, we would go off playing. That was usually the last (for at least an hour) :).
As he knows the consequences, I now go into time out immediately with the first hit, and put the timer on for two minutes. We then talk about it afterwards. Sometimes, he will say, "Mommy, away." and I will acknowledge that yes, mommy had to go away into time out because he hit her. He will kiss my boo boo and give me a soft touch. It's all very repetitive, but it is definitely getting better, and is soooo much more effective than the holding the hands. He is still pushing boundaries, so he will try it at various times to see if I am consistent or not.
Sorry this is so long, but I am in the middle of it, so this is probably a bit more info that you wanted/needed. :) Feel free to message me if you need any support through this.