What is an efficient strategy for increasing my reputation?
Should I: 1. Focus on answering lots of questions, and hoping that my answers float up. 2. Focus on asking interesting questions. 3. Focus on commenting.
Or is should I just “use” the system for x minutes a day, and "act natural"? Whatever that may be…
What is your daily stack overflow usage like?
Definitely answering. Find questions you can answer that only have a few answers so far (or preferrably none) and answer them well. Take the time to polish your answer. Do so iteratively - start with a useful but bare-bones answer, then go through adding examples, links, extra notes etc.
I have a blog post about answering technical questions helpfully. It concentrates on adding value rather than gaining rep, but the one usually leads to the other - and it's just good for the world :)
If you're purely after efficiency, stop answering when you've hit the rep cap. The "effort per rep point" is much higher after that. Personally I'd encourage you to keep submitting quality answers anyway, simply because it's good for the site, but you did ask for efficiency...
I think the most successful method is a combination of various factors:
Contribute in great volume - this will give you many more places to pick up rep. It is much easier to hit your daily cap by answering 10 things a day and picking up 2 upvotes for each then trying to answer one question and getting 20 upvotes.
Contribute quality - Nobody is going to give you rep (in general) if you are not posting quality answers. Take the time to bring good information and insight to the table and you will be rewarded for it. Also, the higher quality the answer, the more likely you will pick up the 15 bonus points for having an accepted answer.
Focusing on commenting will not gain you rep, but it can be useful in bringing more context to your questions. If someone comments, reply back and give more detail.
Take the time to try and answer some bounty questions. You never know when you might hit a bonus.
On meta? Pick a theme... It could be flour-based breakfast snacks, or miniature equines, etc. Wax lyrical ;-p
On SO/SF/SU - simply answer questions well. It is possible to make lots of rep by asking a spectacular non-wiki question, but it is harder.
Rinse, repeat. Rinse, repeat.
You could also peruse the bounty board.
If you are going to hit the rep limit, then knowing when UTC midnight is (in your local time) helps, too; getting 50 upvotes counts for nothing if you are maxed.
Don't post replies that look like spam or which are clearly offensive. In addition to downvotes, you can get hit with a 100pt fine. Likewise, snappish / unhelpful replies ("lmgtfy" etc) can attract negative attention.
Don't be abusive to other site users (or any other kind of site abuse); being put in the penalty box will cripple your ability to gain rep for a while.
It's all about answering questions.
I'd agree with Henk that the best way is to provide good answers to trivial questions fast. And I'd also say that there is a tradeoff between the quality of your answers and the speed with which you provide them. Sometimes a trivial answer to a trivial question can win a lot of reputation. Take this question as an example where a single sentence earned a ton of rep.
Then, there are highly specific questions where to provide a useful answer someone has to
And all this effort that has probably taken some hours and a lot of thinking gets the author one upvote because nobody else reads that very specific question about a Websphere Server on IBM z/OS having trouble to access a certain message queue within the same 2-phase-commit transaction as a database update or whatever.
