Although the HTML title tag isn’t really a meta tag it remains an important factor in how to *improve your rankings*. Its located at the top of your html code between the head tags along with other meta tags you choose to include.
Other than that, most major search engines (including Google) don’t care about meta tags at all. Although one exception applys… Google will *occasionally use the description tag* for the purpose of creating a description for the page when useful or related content can’t be found for some reason … otherwise the search engine will use your sites content and will create one for you.
Including the other meta tags (like the keyword tag for example) won’t hurt your rankings if you are *careful not to over repeat* the same keyword too many times. Repeating more than 2 times may work against you.