What are the 3 most important on-page factors for SEO? Why?

In Search Engine Optimization On Page is very important and Critical.
75% of work is On Page while 35% is off Page.
The Most Important three factors are 1) Keywords Research Selecting the right and related keywords , because if your keywords are not related to your content it will difficult / Impossible to rank a keyword in Search Engine.
2) Unique & related Content As Content is the King in Internet Marketing .
Your content should be unique and relative to your keywords, because it will help in ranking your website.
3) Title & Description Integrate your Important keywords in Page Title and Description , because it will provide strength to your keywords and will be easy to rank your keywords in Search Engine.

As my experience, each factor is the most important one, no one can ignore any of them, when it comes to On-page, we have to care about the user and also the search engine, as I saw many are focusing on search engine, and ignoring the user, where this will lead to a punishment, In my opinion, I sort them as below: 1 - URL : Keywords in the URL & URL Structure 2 - Unique content : Well written with SEO copy writing
3- Well and correct design and coding

3 Most Important On-SEO Page Factors (especially after Penguin etc)

• Your most important and targeted keyword in headline
• Length of content - skimpy contents no longer work to attract Google search. Google loved long detailed contents.
• Relevance

I think all On-page SEO factors are most important as said by my friend ( Abdul Shakoor khan ) 75% of work is On Page while 35% is off Page

Most Important thing is Targeting the right keyword for target page...
Then its related content.
URL structure, and Other factors matters.

3 Main Factors Including: a) Targeting the specific keywords with relevancy to your business industry that should be perfect for Keywords Density.
b)URL structure c) To get business growth, attention and high traffic, website should have 100% original and SEO-based web content.
Have a Nice Day.
Syed Waqas Saghir Internet Marketing Expert, SEO Consultant, Social Media Evangelist.
http://www.facebook.com/syedwaqassaghir http://www.cointelligence.co

Answers provide useful tips, but in my opinion they all concentrate on the well known (or common sense factors), researching keywords, or optimizing meta tags are  SEO101 basics, while unique content is a must, I believe the question is about what are the most Influential on-page factors these days.

In my opinio they are:

 

1- Usability/Content Factors: Time on website (visit time), returning visitors ratio and bounce rate (all affected by good design, page speed and user friendly / usable and crawlable content), text-only version structure is important here.

 

2- Using Schema.org schemas, metadata and rich snippets is a smart approach also.

 

3- Responsiveness: here it means using responsive design and mentality!, keep monitoring, tracking and take an action when needed. (And you will every while for sure).

Title H1, H2 Keywords Description link Unique content

In my opinion optimizing the landing page with keywords and page title the alt tag is important for images the content should be related to keywords and page title