DISCLAIMER: I don't "really" know anything about SEO. What I do know is the folks at Google and other big search engines are just human beings like us who have created and constantly tweak the search algorithms. Their goal is to give us what we want when searching, the best possible websites relevant to what we are searching for.
So let's set aside all the fancy technical stuff and just use some good ol' common sense.
1. Does this page have a good amount of honest information on it about the subject?
This is, by far, the most important one by my standards. I deal with businesses all the time that want to rank higher in search engines but then don't provide any content. If you want to be the #1 search result for "ergonomic loafers", you better start working on a bunch of written content about ergonomic loafers. Good, honest content. Not bullsh*t marketing mumbo jumbo and not keyword-soup. You need research, what they are, why they are good, where you can buy them, every last bit of expert knowledge about ergonomic loafers you can squeeze.
2. Is the information on this page well structured in the markup?
Let's not get too technical here, but just focus on the common sense. When you "view source", is the good content stuff right up near the top, or is it buried way down below a bunch of other non-related stuff? Are the important headers in <h1> tags? Is the title for the page something that makes sense?
3. There aren't any stupid cheap "tricks"
Did your buddy tell you that you should put "paris hilton boobs" in white text on a white background at the bottom of the page so you could get people searching for that? Did you buy some service that promised to submit your sites to 3,253,313 search engines for ONLY $99.99! Did you put 500 keyword variations in your meta tags?
Don't. Search engines are smarter than you. They are looking for dumb "tricks" like that and may even penalize you for them.
4. Is the URL for this page clean and relevant?
You are going to have a heck of an easier time ranking higher for "ergonomic loafers" if you own ergonomicloafers.com. If your page about them is at http://aligatorarmpits.com/2453/234bps.asp?stink=true - it's going to be a lot harder. Common sense.
5. If you were researching this subject, would you find this page helpful? Would YOU link to it?
Take a step back, read the content, think about it. Put yourself in the mindset of a totally random visitor. Is this page useful? Did I learn something about the subject? If my mom emailed and wanted to know something about ergonomic loafers, would I send her this link or would I sent here somewhere better? If I was writing an article about ergonomic loafers, would I link to this?
6. Is the website a reliable source of quality information?
You might notice when googling, uhm, any major subject, Wikipedia articles tend to be around the top. Clearly Wikipedia has established them selves as a high quality source of information.
SEO compounds on itself. You will have an easier time ranking highly for a term if your site is an established and trustworthy source of information.
But I did all this stuff and I still don't rank highly?!?!
Them is the knocks, kid. SEO doesn't happen overnight. It takes a long time. Much of it is based on other sites that link back to your page, and you have no direct control over that. You just need to focus on what you do have control over, which is making your page as compelling as it can be and encourage those links.