This is an easy one - it's exactly how it sounds. On-page factors are things that you can change on the page itself. Things like page titles, description tags, page text, bold italic text etc.
Off-page factors are harder to influence. These are things such as links to your pages and the anchor text that these links use.
More on on-page SEO
On Page SEO - The Basics
Scalable On-Page SEO Strategies
More on off-page SEO
Link Development: The Key to Successful SEO
11 Experts on Link Development Speak Out
When will PR update?
The short answer is nobody knows. Google don't publicise their future updates date. You can see a list of previous Pagerank exports here. Using this we can see that toolbar PR updates approximately every quarter, though this can and does change. - It;s not really worth worrying about though.
How can I learn SEO?
Personally I'm not a big fan of reading forums to learn SEO, there is so much poor information being quoted, that as a newbie it's extremely confusing who to listen to and who to ignore. Some of the best SEO resources that I have seen are,
SEOMoz Beginners Guide To SEO
SEOMoz Serach Engine Ranking Factors V2
SEOMoz Beginners Checklist For Learning SEO
Jim Westergren - Link Building Guide
SEOBook - 101 Link Building Tips to Market Your Website
Ultimately the best thing you can do to learn SEO is to test and re-test things on your own sites. There is no substitute for experience, and over time most of the things in the articles above will be second nature.
Why does domian.com rank? It doesn't have any backlinks?
The chances are that it does have backlinks - you just haven't checked properly. Use Yahoo to check links, Google only show a very small selection.
Sites can rank well even for competitive phrases with only a few very good quality backlinks. The age of the ranking site is also another important factor.
Why does domian.com have PR5, it only has one link!?
That's all it needs. The Pagerank algorithm isn't any secret - in fact it's published here.
The formula for Pagerank is - PR(A) = (1-d) + d (PR(T1)/C(T1) + ... + PR(Tn)/C(Tn))
Which, to put it in a very basic form is,
PR passed to a page = PR of the linking page/other outgoing links x dampening factor (theorised to be 0.85)
This means that all page page would have to do to get to a PR5 is get one link from a PR7/8 page with very few other outgoing links.
How can I get backlinks?
Backlinks can be obtained from many soucrces, some more influential than others. Most backlinks can be broken down into the following areas,
Paid blog posts
Blog comment posting
Some of my favourite linkbuilding articles,
The definitive link building strategy
Link Building Fundamentals: A Primer
What is the meaning of life, and link building?
131 (Legitimate) Link Building Strategies
Quality Link Building
How can I use social networking to increase baclinks?
The two main social networking sites that I have found to work really well for SEO are Digg and Stumblupon. People are correctly note that Digg links are nofollow, but if you're only looking to use it only for the direct link then you're being extremely short-sighted.
Submitting really great content to Digg/SU from a good established profile can mean that when the article goes popular, this results in a huge amount of links back to the original article. This is because a huge proportion of Digg/Stumble users are site/blog owners that use the site for inspiration for fresh news and things to write about. They see your story, they blog about it, they link to it. Personally the best I have ever experienced is 18,000 natural links - priceless as many of them could never have been bought or obtained in other ways.
How can I increase PR?
As I described above, PR increases are solely down to an increase in the PR sum of the pages that are linking to the page in question. To increase your PR get links from higher PR pages.
Why have I fallen down/out of the index?
It happens all the time, don't panic. Hang on for at least a week, the chances are that the site will reappear. If you still don't reappear then go back over any changes that have been made to your site to see if there is anything obvious that has been altered.
Also check to see if you lost any importnatant links.
Does my domain extension .com/.org.edu make a difference?
No, a .com ranks as well as a .info and a .us can rank as well as a .edu. The only reason people think otherwise is that they see lots of .com, .edu and .gov domains ranking well. This isn't because of the domain extension though, it's as these sites tend to be older and have better quality links.
Why am I still not ranking, I have a PR7?
High PR does not equal rankings. It can be a symptom of a site thats ranking well, which is why so many people are under the impression that getting a PR8 is going to be the same as getting to #1 for their search term - but this isn't the case.
Good quality links = rankings (though this is a very simplified way of looking at things), and these usually pass good PR which is why so many people fall into this trap.
Do nofollow links pass PR?
No, they don't seem to, though confusingly Google do seem to follow nofollow links and factor in the anchor text used. Read here and here
Why do my rankings move around so much?
Rankings always change, Google don't have the 'update' that they traditionally used to have, but the search engine results are now in a state of 'everflux' - constantly changing, you'll certainly notice changes each day.
Another reason you'll be seeing changes is that Google data is contained on different datacentres - the results on each of these are never exactly the same, and when you run search queries they won't always query the same datacentre. This is why two people in different places running the same query may well see different results.
When outsourcing SEO how can I avoid being ripped off?
Ask lots of questions, get current client rankings, references and call these people up and talk to them. make sure they have what has been promised to them. Don't just look at rankings, but look at traffic and sales increases - sales is the metric that is important.
SEO Buyers Guide
Google Webmaster Help Centre
Google Webmaster Central
Google SEO Advice Page
Matt Cutts (A Google Engineer) Blog
How to SEO Your Site in Less Than 60 Minutes
The Best Damn On-Page Optimization Process Checklist, Period
An Experts' Guide to Keyword Research
The Ultimate Guide to Make Your Blog Search Engine Friendly
As I could not add links in here ... so I guess for some you have to google .... The write up is not mine ... but it contained usefull info so wanted to share for all those who are interested to learn