Don’t use more words than necessary. Here are a few examples of words that are often preceded by completely–which means fully, totally or utterly. These words are extremes and cannot be made more extreme so the use of completely is unnecessary.

annihilate means to reduce to nothing
destroy means to damage beyond use
eliminate means to destroy so that it no longer exists
ignorant means without knowledge
monopolize means to dominate something by excluding everyone else
surround means to enclose on all sides
unnecessary means not necessary