Short words are best and old words when short are best of all.

So, along with keeping it short and sweet, prefer the familiar to the unfamiliar.

Along those lines, William Zinsser (author of On Writing Well) talks about how he prefers words of Anglo-Saxon origin to those of Latin or Greek.

Watch for Latins and Greeks. After the Normans invaded England, Latin words became preferred by the country’s royalty, clergy and scholars. Latin words were, and still are, more formal and indirect than their dirt cheap Anglo-Saxon equivalents. On the other hand, Anglo-Saxon, the honest language of peasants, packs a wallop. In Anglo-Saxon, a man who drinks to excess is not bibulous but a drunk, a man who steals is not a perpetrator, but a thief, and a man who is follically-impaired is not glabrous, but bald. Direct language is powerful language. Then comes Greek, the language of science. Science is nice. Science is good. But using complicated scientific words can make copy dense and difficult to understand. Moreover, it can make it sound pretentious. Of course you cannot — and should not — drop all words of Latin or Greek derivation from your work. Many times they will be perfect. But first, try to think of a down-home Anglo-Saxon substitute.

Good words, those (source).

I would like to add that almost no one reads long copy. Certainly not on the screen.

So, keep your sentences short. AND keep your whole text short.