What is the most important SEO technique?

As I saw in this forum, there are many SEO techniques but I was wondering which one is the most important when you make a new website?
In my opinion, the main techniques are:
1. URL rewriting, htaccess files, robots.txt files, sitemaps, keywording and meta-tags and all sort of methods like this, that somehow imply "altering" your site with some basic programming or simply editing some files or templates.
2. Link exchange with similar sites. This not only increases your pageranks ( or so I understood at least ) but it also helps you promoting your site to a series of users that represent exactly your target audience if I may say so.
3. Submitting your site in web directories so it could be easily found by people and search engines. This also improves your rankings but it takes some time and it can also cost you.
These are the most important techniques in my opinion. Which one is the most important? And are there others?
Of course, I know that it's necessary to apply all of them, but I was just wondering which one is the most effective.

I am not talking about any SEO techniques.. But here I give you some big factors that plays crucial role on placements of results on search engines.

The biggest factor is Page Title. Every search engines looks on title for first comparison of result.

Then you can consider the domain name. Many search engines are approaching this factor on different ways. Some of them looks for the search keyword on domain, while some other search engines orders the results according to popularity of the domains. Many search engines mix the both for better result.

The next crucial part is the content on the document. The results order according to the relevance of search keyword presence on the page. The page with most repeated search keyword (query) will placed on the top.

Other factors also plays big role on SEO. But these three parts plays the biggest role on SEO.

robots.txt is good for attracting google and other bots and spiders
and once i heard from iven that there is bit fault in using robots
is that true,tell me iven bro

I've put a nice title now for my site. I think its better than any other free downloading stuffs site,but still i hardly get 250/day. Sad!

You must use robots.txt file with your site. That is necessary. But be careful with the syntax you are using.

To know more about robots.txt, visit: http://www.robotstxt.org/wc/robots.html

Now what is syntax n how its related to it? I'm already having Robots.txt in a metatag,as Shadav gave me. I'm already having it,but den too.

Made a file robots.txt and put the following code on there:

This is a simple robot.txt file which allows every bots to go through (crawl) your web pages. You can also restrict the bots to enter into selected pages like logged pages.