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 you're having trouble ranking well with, or if that engine appears to favor pages with shorter titles.