Avoid listing the same word multiple times in a row since some engines may penalize for this. Instead, use the keyword multiple times, but separate them by other words in your text. Use the longer form and the plural form of a keyword when possible. For example, if you use marketing in your Title tag, a search on marketing or market will yield a match on most engines. In these cases you'll want to try and use both forms of the word.
Longer titles are generally better than shorter ones.
However, shorter ones can be used if you need to better emphasize a keyword that is not ranking. All the search engines consider the keywords in this tag and generally give those keywords a lot of importance in their ranking system. In other words, if you were to create one page with a keyword in the title tag, and another page with the same keyword in the body tag, the one with the keyword in the title will rank higher in most engines than one with the keyword only in the body. What this means to you is that this HTML tag must not only work to your advantage for keyword scoring, but also must be compelling to the reader. The site description you offer in the META description tag will be used by some search engines but not by others.