Hi N.,
When my son was 16 months old, that is when I started to put him in time out. What I would have to do was, I would put him on a spot on the floor (the same exact spot every time), and I would literally have to stand next to him (without really looking at him, at least not much.) Every time he started to get up, I would put him right back in his spot. I would have to do this maybe 10 times at first, but after the first few times, he would literally sit there (and cry) the whole time. (I only made him sit there for a minute--now that he is two years old, he sits there for two minutes.) After the first week of standing right next to him, I would start to stand further away from him, like 3 feet away, then 6 feet away, then finally across the room. (Okay, I never measured the distance, but you get the picture.) It didn't take long for him to figure out that he had to stay there, whether or not I was nearby.
Time out has actually worked pretty good. Of course, it's not a miracle, because let's face it, we have TODDLERS, but for the most part it has worked really well with us. It has gotten to the point where all I have to do is threaten time out and he stops. (If for some reason he continues to do whatever it is he is doing, I make sure I do follow up with my "threat" of time out; otherwise, he would think he could get away with anything.)
You really have to pick and choose your battles with a toddler (otherwise, you will be saying NO all day long!); so I just use time out when it is something very very important, such as the threat of hurting himself (like climbing on top of the kitchen table or counter), or if he hurts somebody else (especially his 9-month old sister!)
Our doctor had actually told me that I could've started doing time-out with him when he was 12 months old, like she did with her kids. I just felt that 12 months was too early for my son. I may have been able to get away with it when he was 14 or 15 months old, but honestly it never really occurred to me until he was closer to 16 months old. I am really glad I didn't wait any longer, because some of my friends did and they had a much harder time at getting their kids to sit in time out (my son is so good about it now, all I have to do is point to his time-out chair and he goes right there!) And I make sure that as soon as he is done with time out, I explain to him why it was wrong for him to do what he did, keeping it very simple, and then I give lots of hugs and kisses! You might wanna give this a try...like I said, you may have to sit him back down a billion times at first, but sooner or later, he will get the hang of it. Good luck!