There are several thread on optimizing/building a site to maximize traffic from ALL engines.
An older article written by Brett (which was initally intended as a guide to maximize google traffic, but which I think applies to all engines these days) is
Having said that...here's what I've been doing over the past 30 months or so that has given me both a great deal of non-google traffic, AND the peace of mind of knowing I can live without any one engine's traffic.
1. Outsource content creation:
Use Wordtracker to develop a keyword/phrase list of a few thousand key phrases. From there, go to eLance (unless you would rather do it yourself) and hire a ghostwriter or two to write you some 400-500 word articles based on those keyphrases. INsist that the articles actually be that -ARTICLES. Make it clear that you want info that would actually be valuable to a human, not just gibberish for the search engines. You want to make sure that no matter what, a human reiewer would not see "doorway" page when they look at the targeted content, just a well-optimized article.
Using that method, I add roughly 200 pages per month to our main ecommerce site.
2. Get as many targeted link exchanges as you can.
Notice I said "targeted". Don't link to every gambling, drug or affiliate site that comes knocking. Link only to sites that complement your niche. You'l get less links, but your site will have more staying power. Case in point" My biggest competitor was linking to every Tom, dick, & Harry in the book (he had about 3000 links from every kind of site imaginable). With this update -his site go bye-bye.
3. Use good basic HTML structure (H1 tags, bold, etc.). Avoid all the lousy advice you'll read about "Don't use H1 tags....Don't use ALT text", etc. Use them, but use them properly (i.e. no keyword stuffing, etc.)
Couple the above with some good research on how to utilize PPC to augment you traffic (Note" If the only way you can trun a profit is with free traffic - it's your business that's the problem, not the search engines. You have to KNOW how much each visitor is worth in monetary terms, etc.).
In addition, research sites in your niche (by using the same keywords you are targeting) via google/Yahoo/Msn and see if any of the non-commercial sites in that area offer paid advertising. This can be a great source of cheap traffic (we have a couple of sites we advertise on that turn a profit of $22 for every $1 we spend a month).
Also look into distributing some articles (search for article distribution serices) for some addditional traffic/one-way links. we recently published a series of article that were picked up by over a dozen newspapapers/websites, which resulted in an extra 15,000 or so visitors last month. The 4 articles in question only cost us $300 for a ghost writer to write.
That;s just a few ideas. There are tons more out there...
The key is, avoid the tunnel vision that so many here have of simply doing everything they can to rank well in google and focus instead on making your site the "authority" on it's subject matter. Do that, and the engines will follow.