Try to find keywords where all the top ten hits don't have very high pagerank. It's better to be in the top ten for an uncompetitive word than the hundredth hit for a competitive one, because few people search much past the first page of hits.
As your site's pagerank grows, set your sites on keywords that are more competitive.
Be different than everyone else. It's still quite possible to own a market segment on the net, but most people are not imaginative enough. Anyone with a digital camera and adventurous friends can start a pr0n site, but google says a search for "nude" yields eight million hits, nearly all of which are sites run by people who don't want you to win.
A search for, let me see, "left handed scissors" yields 224,000 hits. Many of them are still people with something to sell, but it's probably not so hard to fight your way to the top of the heap.
Best of luck to you. Webmasterworld is the whole reason I was able to quit my job for adsense this month, about nine months sooner than I thought I had any hope of doing.
It took me seven years to build my site, but I was groping in the dark for most of that. I'm pretty sure that if I had it all to do over again, but knowing what I know now, I could get to my current income level in a year or so.
As long as you don't need revenue from your site to live on right away, don't worry too much about being sandboxed. Concentrate on building quality content, inbound links, and name recognition. There's ways you can get people to talk about your site without showing up in the search engines.
If you can do that, you will find that you spring from complete obscurity into the top ten for a bunch of keywords a few google updates from now.