In the United States and other countries, we elect our leaders. Each individual voter chooses some criteria by which to decide who they vote for, and the aggregate result of all those criteria determines who gets to lead. The public narrative overwhelmingly supports one strategy for deciding between politicians: look up their positions on important and contentious issues, and vote for the one you agree with. Unfortunately, this strategy is wrong, and the result is inferior leadership, polarization into camps and never-ending arguments. Instead, voters should be encouraged to vote based on the qualifications that matter: their intelligence, their rationality, their integrity, and their ability to judge character.
If an issue really is contentious, then a voter without specific inside knowledge should not expect their opinion to be more accurate than chance. If everyone votes based on a few contentious issues, then politicians have a powerful incentive to lie about their stance on those issues. But the real problem is, most of the important things that a politician does have nothing to do with the controversies at all. Whether a budget is good or bad depends on how well its author can distinguish between efficient and inefficient spending, over many small projects and expenditures that will never be reviewed by the voters, and not on the total amount taxed or spent. Whether a regulation is good or bad depends on how well its author can predict the effects and engineer the small details for optimal effect, and not on whether it is more or less strict overall. Whether foreign policies succeed or fail depends on how well the diplomats negotiate, and not on any strategy that could be determined years earlier before the election.
Voters know a lot less about governance than the politicians who study it full time, and sometimes, that leads them to incorrect conclusions. This can force politicians to choose between making the right decision, based on inside knowledge or on complexities that voters wouldn't understand, and making the wrong decision to please voters. It is not possible to know how much should be taxed or spent without studying the current budget in detail. It is not possible to know how banks should be regulated without spending years studying economics. In theory, experts can spread the correct answers to these questions in the media. But neither the media nor the public can tell right answers from wrong ones, and sometimes even the experts and the media have insufficient information. It is not possible to know how much money should be spent on defense without reading classified military intelligence briefings. It is not possible to know which foreign policies will work without talking to foreign leaders.
Instead of looking at positions, look for signs that indicate their skills. Hearing them speak is good, but only when they're forced to improvise and not reading someone else's words from a teleprompter - ie, interviews, not speeches. And be sure to notice whenever they seem to ignore the question and answer a different one instead; that means they couldn't answer the original question. Look up each candidate's alma matter and GPA, if available. If they've held office before, try to find out how much corruption there was under them, and how much of it was pre-existing.
Unfortunately, actually determining how qualified a candidate is can be extremely difficult, we are likely to fall prey to confirmation bias - that is, we tend to emphasize evidence that candidates we like are qualified, and ignore evidence that candidates we don't like aren't qualified. This is especially likely to occur when the information we do have is in a form such that it can't easily be compared. For example, if candidate A held an office and successfully reduced corruption, and candidate B held a similar office but failed to do so, then we should strongly favor candidate A; but what usually happens is that we only have one side of the comparison. For example, it may be that candidate A successfully reduced corruption, but candidate B led a department which didn't have much corruption to begin with, or which was never inspected by journalists closely enough to determine what effect candidate B had. In order to defend against this bias, we should decide how significant a piece of evidence would be before we hear which candidates they apply to.
We should also try to blind ourselves to information that we know will bias us. Unfortunately, the media makes this very difficult; nearly every description of a political candidate will also mention their political party, and this is the one fact we most need to avoid! We need information sources that provide what's actually relevant, and hide what's biasing and irrelevant. We should encourage politicians to take standardized tests and publish their scores. We have sites that help compare politicians' stances on issues; we should encourage those same sites to also provide GPAs and name alma matters, link to interview transcripts, and collect blinded expert opinions on the level of understanding those transcripts display.
Finally, encouraging voters to pay attention to contentious issues encourages affective death spirals, which lead to petty strife and never-ending arguments. Suppose someone starts with a slight preference for party A over party B, and starts studying political issues. They will have a slight preference for sources that favor party A, and party A's positions. Then, when an issue is too close to decide on its merits, they don't acknowledge that; instead, they adopt whichever position their party prefers. Then they go back to compare the parties, and find that party A agrees with them much more than party B does (since their previous information was biased that way), and and strengthen their preference for A over B. In the next iteration, they switch to information sources that agree with their new position, and which are slightly more biased. After enough iterations of this, voters can end up believing that they are informed and impartial, and that party B eats kittens.
Don't waste time arguing about issues which already have entrenched positions, with intelligent people on both sides, unless the issue is actually going to be on an upcoming ballot that you are going to vote on directly. If you're voting on politicians, talk about the politicians themselves - their integrity, their intelligence, and their rationality. That's what really matters, and that's what should win your support.