There's varying levels you can approach a build at. You can dissect choices to spend the least amount of points for the most bang, or you can plan it casually. I'm not a number cruncher, and so I go with what sounds cool. High evasion, attack speed, dual wielding and sword damage, for example. Your character choice affects how much/little it costs you in points to achieve your desired goals. It's cheaper and more reasonable for a Shadow to be what I described above than a Templar, for example, because all those traits I mentioned mostly exist between the Duelist and the Shadow Trees. (I forgo all the traps and ranged combat that are supposed to be the Shadow's signature stuff.) I managed to almost get through Merciless pre-release with that character, and have several more into Cruel. So it's not rocket science.
I tend to shoot for the 2nd tier abilities (the ones between the tiny nodes and the big skills with the orange text) and I seem to do alright. (Although I clearly need to start taking resists more seriously even in normal.) I try to go for clusters that have at least two things I want. And as long as I can take a mostly direct path to them, I make that my goal.
As for chasing life nodes....factor in where life exists relative to the path you want to take. Evaluate if you really want to spend x levels trying to reach that life node if it's not directly on the way to something else you want...or if you need to sacrifice one of your goals in the name of more life, now (since by the time you'll want it, you'll already be getting your ass kicked.)