Which questions have incorrect information? It's hard to answer this without specifics, but we can certainly look at these questions. There's no single best way to correct bad information in a question. Which you choose depends on the exact situation.
Questions are looked at again from time to time, but newer questions do get more eyeballs, dou to the way these sites are designed. (In the event you'd like to ask about the design of SE sites in general, you can do that at Meta.SO.)
There are a few things you could try:
When downvoting and leaving appropriate comments aren't helping, you could try raising the issue in chat. While our chatroom isn't the liveliest, I've gotten answers there to questions about how the community would prefer to handle stuff on the site. Also, you can post in the chatroom, including an @reply in the message with someone's username and they'll get a notification in their inbox about it.
You could start a thread here in meta, explaining your concerns. (Like you've done here.)
In many circumstances, the best way to correct incorrect information is to edit it yourself. You don't yet have the 1000 rep requited to edit others' posts, but you can submit edits for peer review. Respect the original author, and be certain to explain in the edit comments. If what you would have to correct would change the character of the answer, though, this may not be the best option.
You can leave a competing answer. You can get more people to look at your answer by publicizing the question (or your answer, if you want) on Twitter and Facebook. This will, of course, have the happy side-effect of bringing more people to the site.
Sometimes, is't not the answer that's entirely at fault. A question can be badly phrased, and this can encourage quick, incorrect answers. You can combat this by making questions into better questions early on in the process. You can comment on the questions, submit edits to the question, or even vote to close early, possibly with an eye towards re-opening the question later when it's been improved. (Close votes on beta sites currently require 500 rep or higher.)
In the event that information in an answer is wrong enough to harm somebody's safety, please do bring it to the attention of the mods by flagging it. Please use this judiciously, of course!
In summary, there's no best way to handle this, but there are several strategies open to you.
