There really is nothing more important than the inbound link if we are talking about getting a site listed well in the SERPs (search engine results pages). I have seen this proven, time and again, when a site will pop up into a high position with nothing other than a few links pointing at the site from other, relevant and important, sites.
It's important to note that these links we are talking about are one way inbound links. These are not reciprocal links. They are also from sites with a high PageRank or importance and also the links utilize important keywords, i.e., the same keyword or phrase as the listing we are talking about.
Next in importance would be the title tag. I have also seen sites pop into the high listings simply from improving on the title tag. Of course everything depends on the competition levels, the higher the competition level, the more difficult it will be to get listings. I have had good luck with title tags in the 12 word range and using keywords within it that appear on the page within the body content.
I would say the most important things with the title tag is to make sure that the keywords you use actually show up in the content of the site. Don't put keywords into the title tag that do not appear on the page itself. Always spend some time on creating a title tag that is relevant to that particular page.
Next in importance is probably the heading tag. H1 in particular. This should be the most important keyword for the page, and, be what the page is all about. It's not smart to stuff this tag. I have no real proof that any number of words in better than any other, but in general I look at this tag as a title for the page and hence, try to keep it simple and under five words. Often one, two or three words is enough to define the page. Make sure you use the most important keyword for the particular page. Make sure this tag is defining what this page is all about.
The text used in these links should be keyword rich and definitive of the location you are pointing at. Click here just doesn't cut it. You want this anchor text to be informative and define where you are going. That is for the engines, but it doesn't hurt the user either!
I might get in trouble saying that I think code attributes are important. Some folk just don't agree. I have seen some sites rise in the listings after only changing (or adding) the alt= attribute on the image tags. Use your keywords, don't stuff them, and make them relevant to what the image itself is. <em>Consulting Logo</em> is a better alt attribute than <em>logo</em> is.
There is a lot more, and it should be known that everything you do to optimize a site works together... there is no silver bullet, no one thing to do, no magic. It takes a lot of small steel parts to build a skyscraper. It takes a lot of code improvements and linking to build a website. Everything works together the same way 30 instruments can create a symphony, or a cacophony of noise!