On Page Optimisation Factors
In the world of SEO, there are two things that matter. One is linking, which is known as off page optimisation as it is independant of your web site (to an extent), the other is On Page Optimisation factors which you have much greater control of.
The more competetive the keyword you are targeting the less important on page optimisation is but hey, its still optimisation! The cardinal rule is that you must have your keywords where it matters
Title Tag
The most important factor is the title of the page in the head of the document. This is afterall what the page is about. If your keywords are not in the title, it can't be very important can it? Make soure you use your exact keyword or phrase in the title either exclusively or at the beginning of the title. Do not put words in the middle of it to seperate it out, this will dilute the relevancy of it.
Heading Tags H1, H2 (like this one) etc
H1 and H2 heading tags are also very important. Start each page with an H1 tag and use H2 tags where appropriate for sub paragraphs and sections etc. Follow the same rule as your title. There should be little if any difference between your title and heading tags.