Most people believes that search engines and directories are the same thing. But it is not like that. A search engine uses a program that searches web pages, which are mostly HTML documents for specified keywords and returns the list of documents. A search engine has two parts, a spider and an indexer. The spider is the program that fetches the documents, and the indexer reads the documents and creates an index on the words or ideas contained in each document.

But directories doesn't spider or send robots to your website to index your pages. It indexes your pages according to your submission and their guidelines. Some famous know are DMOZ or Yahoo. When you go to a directory you go to their appropriate category page and submit your website with appropriate title and description.

As search engines see your websites from a completely different angle of a directory you need to take care of the following things meta tags, alt tag (alternative text for your images), title, content (key word density) etc. Directories just simply values your title and description and if you submitted within their guidelines they are most of the time happy with that.

What you need to do when submitting to a search engine?

First of all make sure your content is well written and keyword focused. If your site is about gardening make sure you have spent enough time in researching about it and wrote a content where the word gardening holds a good density. This is called the key word density. Now other things you should focus is your meta tags like description met tag, keyword meta tag. Make sure you have title tag, alt tags etc.  

So in your next step you are going to submit to search engines. If you are hard worker then it is preferable that you manually submit your site to the search engines. Go to Google search and check "submit url to google/msn/yahoo" and the result will take you to the search engine submission location. If you are not very sure then check global submission, Doorway Pagemaker or Indeedhits for paid and easy submission. 

After you submitted your website to search engine it will take some time for search engines spiders to crawl your site and index it. Don't submit again and again to search engines to get quick results because it will be considered as Spam by search engines and your website might not be indexed.

When you are submitting you site to search engines also submit to directories because they will also give you some targeted traffic.

Resubmit to search engines only when you make some major changes in your website.