If you see other people lagging, then there character will end up running on the spot and jittering there for a moment... until they suddenly disappear and reappear some place else. That isn't you lagging, that's just how the server interprets when someone else is lagging.
If YOU are lagging then your own movement becomes choppy, really, REALLY choppy and the game becomes uncontrollable at some points and you think "how am I going to play this? I can't even get proper control of my character"...
So don't worry if you see some others running on the spot for some reason. Just as long as your character control feels fluid and normal, that means you're good.