I started working with Adsense on October 19th, 2005. As of yesterday, April 22nd 2007 I finally had my first $100 day. I know there are people here who average more than that but for me it's a milestone and I want to celebrate (Margarita's tonight!) I also wanted to give something back to the webmaster community. I know I haven't posted much here but I have lurked quite a bit and it's been helpful.
What has helped me... Maintain site maps and keep them up to date
Cultivate visitor loyalty - most of my visitors (usually around 2/3) are people using bookmarks to come back
Make content that people really want to see
When I see a way to do something better than what is currently available, do it.
When I see a way to substantially improve what I already have out there, do it (but sometimes this has backfired)
Keep 4 or 5 new things in the pipeline at all times. The cycle for my content is typically a month or two of slow build-up, then a quick (100 ~ 300%/week) spike, followed by a small decline (~ 10%/week) and then a plateau. The best content I have continues a gentle rise from the plateau. Lesser content tends to have a sharper decline after the peak (20 ~ 30%) followed by stagnation or a gradual decay. Once I had enough new stuff in works I started getting a steady stream of peaks which seem to make the daily revenue more uniform.
What did not really help me... Link swapping with other websites
(I realize the things which did not work out well for me probably do great by some people.)
Attempting to manipulate search engine results by artificial means.
Using ads to drive traffic to my sites (I turned $50 into a nickel in one day)
Banner ads across the top of a page (thousands of impressions, no clicks)
The Adsense "heat map" - my best results are coming from sites with navigation on the left, content in the middle and single a column of ads on the right of tall pages or a single rectangle in the upper right corner of shorter pages.
Excessive number of ads per page. At first I was putting them everywhere possible but in my case too many ads seemed to be causing a decline in the number of return visitors
Attempting to perform well with "high paying keywords" by covering topics that I am not really passionate about. I just don't care much about asbestos and structured settlements
If all I can do is make something the same as what is currently available, don't bother; my "me too" sites have never run a close second, more like 999th.
About the work... I typically put in two hours in the morning, two hours in the evening and about 10 ~ 12 hours each weekend.