This is very important. Keep common word groups or phrases that people might search on together if you can. Keywords that are more prominent will be weighted much higher with the search engines. Most engines rank you higher if the keyword or phrase is near the beginning of the title and as close to the beginning of the page as possible. Keep your pages short while including and repeating keywords frequently, particularly in the first 3-5 lines of the pages.
Some engines ignore or largely ignore wording beyond the first paragraph or two.
Having a short page goes much farther to improve your rankings with many engines than you might think, even if the keywords are not repeated very many times. Unfortunately, what is appealing to the search engines is not always the best way to display the content for you Web site. Therefore, strongly consider creating a secondary page for each product or service you offer designed for the search engines. The reason this works, and generally works better than most methods, is that engines often take the keywords being searched and divide it by the total number of words in the page or in the first portion of the page. You don't have to have links to these secondary pages from your home page.