When i started in adsense i was told i needed a large number of sites all built to make at least .25 per day. I was told by many ebooks and other adsense sources that 100 sites all making between .25 and $1 was the easiest way to keep the money rolling in. I tried this method for a while and eventually got myself up to 21 sites. Some sites made good money others made no money at all.
While alot of sites making a little money sounds like a good practice on paper found this method to be more work then it needed to be. Trying to article market 21 sites was hard to do and as i monitored my sites traffic i would often try to blast five articles into the article directories for any sites that had falling traffic. I found that after 20 sites it became to hard to do this with limited time and i had to scale back a bit.
I took my five most profitable sites and started to concentrate on those. I will write 1-2 articles per day and write them for a different site each day. This not only keeps a steady flow of articles going but it is also brings each of the 5 sites more traffic and my earnings are increasing faster then when i was just slamming up site for the sake of getting them up there.
I still have all 21 of my sites up and some bring in a few dollars a month so i leave them up. But i really do not do to much to promote them. If i can get my earnings up to $50 a day i may start to out source article writing to bring the older sites up to speed, but everything in time!
The key is to get the niches that pay the most so that every click counts. I never reveal my niches but i will say that sticking with areas that have large corporate advertisers is gonna make you the most.