Steps inside the elevator don't count. If you run and jump out of the elevator, it only uses 1 step (if you don't move forward when you land).
Falling from one portal into the other is very useful and uses no steps. With forward momentum and perfect portal shooting, you can chain a series of portals so that you jump into one on the floor, come out of the ceiling ahead, shoot and fall into one further ahead on the floor, shoot and fall out of one further ahead on the ceiling, etc. (YouTube example for #1 and #2)
As you mentioned, portal placement. A lot of the levels can be navigated around with only a couple steps if you're "thinking with portals".
Those are how I got all the gold achievements for steps in Portal, nothing more complicated.
This should work in both games. I believe you have to re-enter these every level, as you'll spawn in first person mode.
However, this will probably disable your ability to get Steam achievements for the games, so that's probably not the best idea. ModDB lists this mod for Portal 2, which should accomplish something similar. I haven't seen anything similar for the original Portal.
If you get vertigo, Portal games might not be for you - your perspective shifts frequently, and what's up is frequently down or sideways in rapid succession. The shift to third person might work OK in most other games, but you might find that Portal causes you more problems than other games.
Best Answer
Here you can find them all: http://www.portalwalkthroughs.com/
You can search for the one you want, or watch the advanced ones that are all in the homepage (scroll down a little)