All the major search engines take account of the different parts of your web pages. Since - at least in theory - you have total control over these factors, it pays to make sure that as lots of as feasible are correct.
1. Title tag
This is the title of the page. It appears at the top of the browser screen you are on as well as in any tabs you have open. It is also the blue clickable link that you'll see in the search results. Which makes it one of the most important tags you can use. Each page title ought to be crafted for the content of the page, ideally with the most important keywords closer to the beginning of the title. The maximum length displayed in search results is around 65 characters.
2. Description tag
This is sometimes used by the search engines for the main text below your title link. Make it nice, with either a teaser of what your page is about or some kind of call to action. The maximum length displayed in search results is around 160 characters. Keep in mind that search engines can select to make use of other text from your page if their algorithm decides that will better serve their users. If you are lucky to have a listing in Dmoz or the Yahoo! Listing, this description is sometimes used in lieu although you can over-ride that by using a meta tag in your pages to tell the robots of your choice.
3. Keywords in your URL
In the event you can pick, it is usually thought about nice to make use of your keywords in your url. The major search engines bold the keywords in their results to give searchers confidence in the results they have been given.
4. Heading tags
After the title, headings are one of the most important on page SEO items. Think of them in much the same way as you'd see headlines used in a journal story. One main headline (the H1 tag) and a few other sub-headings. If your page layout looks messy with the default heading size then you can use CSS to change it so that it fits better with the remainder of the look and feel of your site.
5. Picture names
You have probably noticed that the search engines offer an picture search and that images sometimes come up high in the results, depending on what you are looking for. Because analysis of the contents of images is still in its early stages, sensibly naming your images and giving them significant "alt" tags helps the search engines to correctly classify them. It also reinforces what your page is about. So take the time to change the name of your images from the default numbering system used by your digital camera to something that a human (or a robot) can understand.
6. Write naturally
Don't stuff your page filled with keywords! That might have worked in the early days of the net - back when Google was a twinkle in its creators eyes - but it will work against you nowadays. Write for humans first, search engines second (if at all). The search engines have analysed literally billions of pages of text and know what words are related to other words, even down to the context. So if you are speaking about an apple on a computer page it will be given a different intending to a maths issue page or a healthy eating page. The search engines are usually smart to work this out. So write naturally and let the robots figure out what you are page is speaking about - most of the time they'll get it right.