First of all, it takes time for the search engines to crawl your entire site, index it, and rank it. If your site has been acquiring backlinks to it, it takes time for the search engines to find these backlinks. A typical time schedule for a new site to begin ranking in the top 50 or top 100 is around 3 months. You might do better than that if the subject matter is not very competitive. It might take quite a bit longer for a very competitive topic.
Once your site ranks at all, then begins the process of tweaking and building backlinks....waiting for the results...tweaking some more...getting more backlinks...waiting for the results...etc. I always assume a new site will take anywhere from 3 to 6 months before it has a chance of being in the top 10, and that's with hard work being applied the entire time. If I get lucky, and the site ranks well before that, then that's a bonus, not an expectation.
It can often take Google a couple of months to assign your new site any PR, or show any backlinks when using the link: operator. So don't panic if after 3 weeks of putting up a new site, you don't see PR or backlinks right after a PR/BL update. You'll probably see it after the next update. Again, Patience is the key here. While you are waiting for the search engines to recognize what a brilliant site you've made, use that time to add new content, gather new backlinks, and work on your on-page optimization.