Diagnosis: Big words when smaller are better, long clauses, imprecise wording, mixed metaphors and inaccurate similes all make for unclear prose. Readers come away feeling like they need to clear their heads.
Cure: One way to fix lack of clarity is knowing what you want to say even if you're still figuring out how to say it. Let's start by defining metaphors and similes. A metaphor is a word or phrase that's used instead of another to suggest an analogy, for example, "drowning in money." A simile is figure of speech, often using "like," that compares two unlike things, for example, "cheeks like roses." These tools for writers need to be used correctly (in the right place at the right time) in order for them to function as they should.
As with wordiness, cut unnecessary text, use contractions for less formal prose and expand your vocabulary to make one word count for more. If you're still deciding what you want to say and how to say it, ask yourself what the scene or story is really about. Why did you create it? Then consider how it can be revised to reveal character and advance plot, preferably both.
For a great pro at editing, visit James Scott Bell, or check out his book Revision And Self-Editing (Write Great Fiction).