It's the big day. Voters are at the polls, campaigns are holding their collective breath, and we're all getting ready for the first returns early Tuesday evening.

But once those returns start coming in, how does one even follow along? What are the most important things to keep an eye on?

Below are six key things to watch for.

1. The majority-makers

Republicans need to gain six seats to win a Senate majority, and they are clearly favored to win five -- Montana, West Virginia, South Dakota, Arkansas and Louisiana. That would mean the GOP, in the rest of the top 13 races, needs to register a net gain of one.

As long as Republicans don't lose Kansas -- their most likely Election Day loss -- that would mean winning at least one of five races: Alaska, Colorado, Iowa, North Carolina and New Hampshire. Those are the majority-makers, and Republicans appear to be narrow favorites in the first three.

If the GOP does lose Kansas, though, it'll need to win two of those for insurance, given it's not clear with which party Kansas independent Greg Orman would caucus.

This is how the battle for the Senate looks, at its simplest. These things, though, are rarely so simple.

2. Does the race end on Election Day?

In short, it's quite possible that it won't -- at least when it comes to the Senate majority.

All of No. 1 assumes that Republicans will win Louisiana. But they won't know that for sure until Dec. 6, because the race is almost definitely headed for a runoff, with two Republicans currently splitting up what would be a majority share of the vote.

And while Republican front-runner Rep. Bill Cassidy would definitely be a favorite against Sen. Mary Landrieu (D-La.) in a runoff, the GOP would prefer that the race didn't make or break their majority. For them to truly rest easy after Election Day, Republicans would like to win two of the five majority-makers above and avoid a loss in Kansas, or win three of the five if they do lose Kansas.

And that's all assuming that Democrats don't push another race to a runoff, in Georgia. If they do that, the GOP would really need to run the table on Election Day in order to render those runoffs moot.

Even if it comes to that, though, Republicans would be favored in Georgia as well -- especially if that red state becomes pivotal for the Senate majority. It's hard to see Democrat Michelle Nunn pulling an upset on Jan. 6 -- less than a week after the New Year's holiday when turnout will be tough for Democrats -- in that scenario.

In sum, there are plenty of scenarios in which the GOP's majority hopes remain uncertain beyond Election Day. And here's one more...

3. Waiting for Alaska

Whether or not we find ourselves waiting on Louisiana and Georgia, it's quite possible we'll be waiting on Alaska, at least for a few days.

That's because polls close very late (midnight Eastern time in most of the state and 1 a.m. Eastern time, Wednesday, in one precinct in the Aluetian Islands in the state's west), and mail-in ballots will be accepted as long as they are postmarked by Tuesday. Such ballots won't even be counted until next week, so if the race is even a little close, it's unlikely it'll be called in the next couple days.

Sen. Mark Begich's (D-Alaska) 2008 one-point win over then-senator Ted Stevens (R-Alaska), for example, didn't conclude until more than two weeks after Election Day.

In other words, don't plan on going to bed Tuesday night knowing whether the GOP will be in the majority.

4. Independents' Day?

Tuesday could be a big day for political independents -- in a number of ways.

Of course you've got Orman potentially upsetting Sen. Pat Roberts (R-Kan.) in the most surprisingly competitive race of the election cycle. If Orman were to win, it would set a record for the number of independents in the U.S. Senate, at three.

Orman, of course, was aided when the Democratic nominee dropped out of the race. What many people don't realize is that a very similar thing happened in the Alaska governor's race, where the Democratic nominee dropped out to become the running mate for independent Bill Walker's campaign. Walker, like Orman, appears to have a very real shot at upsetting a previously un-targeted GOP incumbent, Gov. Sean Parnell (R).

If he were to win, Walker would become the only independent governor in the country and would only be the third pure independent to be elected governor since the 1970s.

If both he and Orman win, expect the two parties to try and emulate this strategy in races that would be lost causes to one of their nominees.

5. A historic GOP House majority?

If the GOP takes the Senate, the big question will be whether this was, in fact, a wave election. A big argument against the "wave" designation will be that Republicans are unlikely to win much more than 12-15 House seats, even if it's a very good night.

Of course, there's a pretty good reason they can't win more: They're pretty close to maxed out. Their 234-seat majority (including one vacancy in a GOP-leaning district) is one of the biggest in decades already.

In fact, if Republicans win 12 seats on Tuesday and get to 246 seats, they will tie their biggest House majority since the late 1940s. If they won 13 seats, it would be their biggest majority since the Great Depression.

Much of the reason for this potential history-making majority is that Democrats so dominated the House for many decades in the 20th century. But that doesn't mean it wouldn't be significant.

6. Gubernatorial upheaval

This is both a real possibility on Tuesday night and also a great potential name for a prog rock band.

It's very unusual for an incumbent governor to lose on Election Day. In fact, since 1984, the most incumbent governors who have lost in one election was six.

Well, according to the latest Cook Political Report race ratings, 10 incumbent governors find themselves in "toss-up" races and one, Pennsylvania's Tom Corbett (R), is considered a goner. In addition, another incumbent governor -- Hawaii's Neil Abercrombie (D) -- already lost his primary.

And despite the GOP's momentum in the House and Senate, eight of these vulnerable governors (including Corbett for the moment) are Republicans.

So talk all you want about how people are upset with Washington; there's likely to be even more turnover in the ranks of the nation's governors.