Let me tell you that I am really really upset at miss information online when it comes to off page and on page optimization. I have recently heard one person say to a complete newbie to SEO, “don’t worry about on page optimization, off page optimization will be enough”! I have to say, plain and simple that is not true unless you have time to waste. Here is why!
Optimizing on the page for the certain keywords is there for a reason. You optimize the page for certain keywords. That is like placing an ad to sell a house, you want people who are interested in buying a house to find your ad and not those who are looking to buy a car. So with on page when you optimize you are actually optimizing and letting people know what your page is about.
This also tells search engines what your page is about. However, in early days of the Internet, building backlinks was NOT important as much, because search engines did not have any rules to follow, however that has changed a lot since. Now search engines have certain rules about who gets to be on the first page.
So that is where off page (link Building) comes in. You need to build xxx numbers of links (or outsource link building to someone) with anchored text with those keywords in order to rank high.
However, keep this in mind, when you are NOT doing on page optimization but are concentrating on link building, you will have to build many more backlinks then you would if you have done the on page optimization. Because you are confusing search engine with NOT doing on page optimization.