Generally speaking, we disambiguate by the first story a person or thing appears in. However, this isn't usually practicable when an alternate timeline, parallel universe or a pocket dimension is involved.
Multiple versions of same person often introduced in same story
It's important, therefore, to disambiguate on the basis of the entire location, not just the story — even if that means creating a name for the world. Hence, Greg Sutton (Inferno Earth) achieves the goal of clarity. Equally, so does Pete Tyler (Pete's World).
Historical figures in alternate realities
Another good reason to disambiguate by a named reality is the case of the historical figure. Often, realities become "alternative" because someone famous is said to have done something different than what they did in our "known" universe. The famous person may not even make an appearance in the story, so you can't use the story name as a dab term.
A good example is Adolf Hitler (Inferno Earth). He doesn't exactly appear in the book The Face of the Enemy, but his legend on Inferno Earth is described. A name like Adolf Hitler (The Face of the Enemy) wouldn't make nearly the common sense of Adolf Hitler (Inferno Earth).
In order to make these pages easily discoverable by other readers, it's important to stick to one term to describe all people from a certain reality. People from the main DWU reality either have no disambiguation term (if their name is sufficiently unique), or are disambiguated by the name of the first adventure in which they're seen.
Choosing a good name for the universe
Finding an appropriate universe name isn't easy. On rare occasion, the script will offer it up. "Pete's World" is the perfect case in point. The Tenth Doctor actually says it in the script, so that's what we go with.
On other occasions, the best we can do is to make a logical in-universe inference. Hence, Inferno Earth is based not upon the story Inferno, but rather the in-universe concept that gives the story its name: the Inferno Project. We give it that name because the Doctor accessed that universe via the Inferno Project itself.
You should try to base the name on some sort of in-universe concept where at all possible, so that the name can be used in articles without fear of introducing an out-of-universe concept.
If you're really stuck trying to figure out a good, in-universe name, ask for naming help at Board:The Panopticon, or to grab an admin. Note, though, that there may be some cases when we have so little information about a particular alternate dimension that we may have to resort to out-of-universe nomenclature.