We generally ask for a gate check tag as soon as we arrive at the boarding area and there is someone staffing the desk. If you don't do this then you will have to as you are trying to board the plane... and hold up the line.
Once we are boarding, we push the stroller to the end of the jetway, where it turns right before you actually board the plane, and leave it there.
It is always waiting for us in the exact same place when we get off the plane at our destination...sometimes it's opened, sometimes it isn't.
HTH