On the other hand, there’s also plenty of hype that should be heavily discounted. The press has an interest in a horse race in which something happens, so there’s a major bias in favor of seeing twists and turns. That’s already happening. Marco Rubio is collapsing because of immigration! Ted Cruz is surging because of a great appearance in Iowa! Chris Christie and Rand Paul are feuding — and maybe that sinks Christie!
So what should we take seriously?
Ignore the candidates who lack conventional qualifications for the presidency or are outside the mainstream of their party.
Pay special attention to anything concrete: full-out endorsements especially, but also money raised, staff added and other tangible indicators.
Mostly ignore the polls. At this point, they’re mostly name recognition; even when we get close to the primaries and caucuses, short-term surges and collapses, usually pegged to short-term news cycles, are not unusual.
Be wary of “rules” that supposedly govern who wins. No, Republicans don’t always nominate the next in line. Even “conventional credentials” and “mainstream” — the rules I’d suggest — are purposefully vague, because some cases really do seem borderline.
Beyond that, there’s really no rule of thumb; there’s just judgment about what’s real and what’s hype. This isn’t like presidential general elections, where we can expect the fundamentals to kick in; there’s really no way to know who emerges from Christie and Rubio and Cruz and more. I would be wary of “tiers”, such as Larry Sabato’s groupings; unless there’s some clear criteria that make sense, it’s a fairly arbitrary way to sort the candidates.