However high or low your page is in Google's rankings, more people will visit your site if the text that appears in their search results interests them. How does Google determine what text to display? What can you do to control it?
Obvious things first: The link text is taken from your page title. If your page title is too long, it will be truncated at about 70 characters. Be sure to say something interesting in the early part of your page title.
Now on to the interesting stuff: where does the text under your page title come from? There's no one answer, and in fact, different text may be shown for the same webpage depending on the terms that were used in the search.
Google's first priority appears to be displaying text that includes the search terms. If the search terms don't appear until late in your page, then text from late in your page will be displayed. If the search terms appear in various parts of your page, snippets from different parts of your page may be displayed.
If the search terms are found in your meta description tag, that appears to be their first choice for which text to display. One important thing to note is that if Google wants to display part of your meta description tag along with text from elsewhere it your page, they appear to prefer to stop displaying text from the meta tag at the first period. To increase the probability of the whole meta tag getting displayed, use punctuation other than periods between sentences.
After the meta tag, text appearing early in the page body is more likely to appear than text appearing later in the page. Also, text where all of the search terms appear close together is more likely to appear than text where those terms are further apart.
So how do you control what text appears in Google's search results? Make sure the search terms you are optimizing for appear close together early in your meta description tag or close together early in your page. If your site navigation appears above your content, put it at the end of the document, and use CSS to position in higher in the page instead of putting it at the beginning of the document. Then, hope that people use the search terms you're optimizing for!