The Keywords tag
<meta name="keywords" content="some keywords">
The words in the Keywords tag were never treated as keywords by the search engines; they were treated as text on the page. The tag isn't as effective as it used to be but there is no reason to leave it out. So put plenty of relevant keywords into the tag and include the search term once at the front, and a second time further along the line. There is no need to seperate keywords and keyphrases with commas, as is often done, since the engines ignore commas.
The H tag
<Hn>some heading words</Hn>
"n" is a number from 1 to 6; the biggest heading size being 1. H tags are given more weight than ordinary text and, the bigger the H size, the more weight it receives. So include the target search term in H tags at least once on the page, and two or three times if possible. Also, place the first H tag as near to the top of the page as possible.
Bold text
Bold text is given more weight than ordinary text but not as much as H tags. As much as is reasonable, enclose the search term in bold tags when it appears on the page.
Text
Use the search term as often as you can on the page whilst not detracting from the page's readability. Make sure that you use the term once or twice very early in the page's body text and as often as possible throughout. Reword small parts, and even add sentences, to make sure that the search term is well represented in the text.
In all probability, each word in the search term will be found on the page seperate from the search term itself. This is good. In fact, if they are not there on their own, add a few of them through the page.
Alt text
<img src="url" alt="some alt text which is displayed on mouseover">
Include the search term in the alt text of all images on the page. Keep in mind that some systems such as Braille readers and speach synthesisers use the alt text, so you might want to make them usable whilst including the search term.