From my point of view, it seems that a lot of parents often forget that children can be very different, even at the same age. It's easy to say "yes, of course the same thing won't work with every child!", but it seems that often people will stop right there, and not consider the reason that some children are different and that the answer "just try Y instead of X" isn't always an option
This is true to an extent. There are a lot of differences among children, and anything you do has to be tailored to the nature and personality of your child.. However, there are also a lot of similarities. Children respond well overall to limts being set and enforced. So set limits. Explain the limits.Enforce them. Explain again (after they're enforced). Because if you don't enforce them, you teach that your limits aren't really limts at all, and they keep pushing them further out. It doesn't mean they won't push them anyway but a consistent response means they know how far they *can* push and what's ok.
When I was a kid (I'm 35), TV time was very limited, especially during the day when there were other things we could do. When we finally got a computer, time on it was limited as well. I even remember wanting to be outside with my Dad over watching daytime cartoons or whatever. It's not choosing the great outdoors over technology, and I hope you realize this.
Of course I do, and that is a valid point. My son is an active boy, but even so I understand that were the choice different - for example, TV with Dad vs outside with Dad - the answer might be different as well. Because when it's "with Dad" in either case, it boils down to whatever the child prefers to do. But my point was that to encourage time outside, I don't give the choice of TV with Dad in most cases. Instead it's time [by himself] using electronics, or time [with me] outside doing stuff.  And to a three year old in that's no choice at all - no matter how much he loves watching Bob the Builder.
 - most children will push limits. hell mine thinks it's awesome to start sticking appendages into a room I've told him he can't be in. The intent is clear: "you told me I can't be in the kitchen right now, but I'm not - I'm exactly on the threshold and my *hand* is in the kitchen".
 -. The answer to this (again in my experience and in my observations) is not to make every limit an absolute thing, except in areas of safety where failure can mean serious injury [2.1]. Set the limit. Know *in advance* how far you will let them push it, and the reasoning behind it (because they will ask and you should have an answer -- after they listen, or else it turns into a negotiation.)
[2.1] No he may never run away from me in the parking lot. Ever. Immediate response to any attempt to do so. On the other hand: I will warn you against the consequences of standing on that stool on the carpeted floor -- but I will not stop you from doing it. Nor will anybody comfort you when you fall down and get hurt. I'll warn you of that, too.
 - I say unequivocably enforce limits. This doesn't mean demand instant obedience, but rather know the limit you want to set, know how far you will allow the child to push that limit - and be consistent.
 Giving choices - even rigged, loaded choices - is a really important part of parenting, I think. (Perhaps especially the rigged, loaded questions) It took me a while to learn that. Longer still to learn that even very young kids can understand reasoning and choices fairly well. Much better to say, "You can stay here and watch TV while I work in the yard, or you can come outside with me and help." As opposed to either a) not giving the choice because it would much easier for my life to get the yardwork done alone, or b) simply dictating "thou must exit the house fortwith and accompany me now - so sayeth the Lord Dad Thy Father"