DISCLAIMER: there might be errors in this article, do your own due diligence and verify the information.
What are curation rewards?
A reward you receive when you vote on a post. At least 50% of the rewards always go to the author, the other 50% is divided between the author, the curators and the commenters. Curation rewards are paid out 100% in STEEM POWER, which increases the power of your up-votes, so you help the content creators and yourself!
What does it cost to vote?
Nothing except your time.
So then i can just vote 24 hours a day and get rich?
Nope, there's something called voting power, which decreases your curation rewards every vote (although it seems to be every 5 votes for me currently). Apparently it's beneficial to vote at least 20 times a day.
Voting Power regenerates at a fixed rate over 5 days.
Posting Reward curve is now R2 + 2RS rather than R2 and a relatively small value of S was chosen.
So what's the best strategy then?
There's one more extremely important factor:
If you vote immediately after a post is made, then 99.94% of the curation reward will go to the author. If you vote after 15 minutes, then 50% will go to the author. Any votes made 30 minutes or later 100% will go to the curator.
The ideal situation for maximum rewards is voting on a post that is at least 30 minutes old, has only 1 vote from the content creator and ends up making $50,000. Unfortunately that happens very rarely. To receive the best rewards, you have to assess the quality of the post and monitor the amount of voters that came in in the first few minutes. If there are a lot of votes in the first few minutes you might want to get in way earlier than at the 30 minutes mark. It's all trial and error what works best for you.
Also keep an eye on your voting power by visiting http://www.steemd.com/@username where username should be replaced with your username. The farther it is away from 100%, the faster it regenerated, but it always takes 5 whole days to regenerate completely to 100%.
Sources:
steem-0-8-0-released
Whitepaper