I notice some users with very high reputation scores. What is their "trick", and how can I increase my reputation?
1. Ask Good Questions
Firstly, ask good questions. Good and thorough questions are more likely to be upvoted to increase your reputation. When you ask questions you learn to, so you can help other people on the site with similar problems.
2. Edit Tag Wikis
Secondly, edit tag wikis. This is something that anyone can do with access to a search engine and some time on their hands. Adding descriptions to tags that don't have descriptions already will help you further understand Ubuntu and help other people to learn about terms that they don't already know. You can edit tags by clicking on the "Tags" link in the top navigation bar.
3. Leave Helpful Comments
Thirdly, leave thought-provoking and helpful comments. Don't be so critical to the point of being annoying. Leave a comment if something needs to be clarified, this will help the asker of the question so that the people who are trying to answer further understand the problem. Don't leave comments saying that the asker did a good job on their question, instead, upvote.
4. Be an active user
Fourth, be an active user of the site. You get badges for leaving so many comments, upvoting so many times, visiting the site for so many days in a row, etc. For more information on what badges you can get for doing what, go to the "Badges" tab in the top bar. Read other people's questions and maybe they will help you learn something.
5. Give Detailed and Easy to understand Answers
Fifthly, Give quality answers to questions, Try to give answers after you actually do researches with them, tested them or at least confidence with them. Try to give instructions as clear as possible. Give several options for answers, if they exists. And Revise your answers as new information arrives. Also, always keep in mind the questioner's knowledge level with Ubuntu, so give answers accordingly.
You earn privileges for gaining rep. The more rep you have, the more stuff you can do. Remember that the FAQ says that "reputation is a measure of how much the community trusts you". In real life, building up trust takes time. Gaining a high reputation is going to take a lot of time and effort. Take some time and read through the whead the FAQ for some more ideas on how to gain rep and use the site appropriately.
Unfortunately the most efficient way to farm XP is to rephrase existing simple answers on easy questions while the question is still hot. Long detailed answers on difficult questions are not worth much because too little people are interested in them.
Edit: This is based on my observation on StackOverflow. There is, however, one important difference between StackOverflow and AskUbuntu: SO has so much traffic that questions only stay on the front page for about 10 minutes after the last answer.