Google's ranking factors are plentiful and one of if not the most closely guarded secret of Google themselves. It is because these factors are kept a secret that no one is able to exploit them in order to tip the search results in their favor. Here are the various Google ranking factors to keep in mind.
Authority of Domain
This is the biggest one and this is really just a general snapshot of your site. It takes into account other factors to give your site an overall score of authority and every web page which you're trying to rank on your site is going to be affected by the domain which it is attached to. The more authority which your site has, the stronger each page on your site will rank on its own and the stronger which your internal link juice will be. How much content you have on your site is another factor. Content sites are going to trump mini sites (Add Link) as a reflection of your site's authority.
External Link Anchor Text
This goes with the next Google ranking factor, but the anchor text which you use from other web pages off of your site to point back to your site helps Google identify what your page and its content are about, so getting as targeted as possible is great.
Strength of External Links
The authority and PR of any sites which link to you has a substantial effect on the strength of those links. A PR 6 site linking to your site will be a major boost for not just the page which is being linked to on your site but for your entire site as a whole as this adds to its overall authority.
Conversely, if you have a number of spammy links pointing to your site then this can have an adverse on your site's ability to rank.
On Page SEO/Keyword Usage
I made an entire post about on page SEO factors. It's important to refresh yourself with them if need be because while they're very simple to implement (which I also explain in that post), they have a substantial role in your ability to rank for a keyword, so you can't overlook their importance. Just as important is to include LSI keywords (Add Link), or variations/synonyms of your keywords on your page so that it looks more natural to the search engines.
Social Search/Proof
Social search and social proof are two more substantial factors which I've actually been predicting will play an increasing role in SEO. This is such an important Google ranking factor because social proof is actually people vouching for the validity and quality of your content, so having your website and its content be given a thumbs up from Google's own users tells Google that you've got something worth ranking and ranking well at that.
Traffic + Bounce Rate
The amount of traffic which you get to your site is another metric of its quality, so this is another one of Google's ranking factors. Bounce rate is another factor because if everyone who visits your site leaves just as quickly without visiting another page, that is evidence that you're either not optimizing your site correctly or your site and its content are both low quality, and Google may assume it's the latter.
Registration/Hosting
Does hosting affect your rankings? You bet it does. For example, say you have a cheap hosting provider which experiences a lot of frequent outages (why are you still using them by the way?). Google doesn't like sites which have difficulty staying online because this creates problems for its users who are trying to reach your site. If this happens frequently you can drop in rankings.
If your site is down a lot, sites which link to your site may pull out those links which would undoubtedly cause a drop in the SERPs for you, as well.
Also, if you're on a shared hosting account with a spammy webmaster who is constantly spamming people, if that site gets complained about enough and finally tagged and penalized by Google, it's possible that you can feel some of the impact.
