Avoiding Formulaic or Weak Writing

Note: The lists that follow are only partial.  There are hundreds, if not thousands, of examples of each in the English language.  If in doubt, look it up.

Cliches: Overused or tired expressions. They've been used and heard so often that they rarely contribute to fresh, original writing.
Examples Examples Examples
Abandon ship Back against the wall Call it a day
Ace in the hole Bank on it Cat got your tongue?
At the drop of a hat Beauty is only skin deep Chew the fat
Asleep at the wheel Better than ever Cold as ice

Jargon: Special language belonging exclusively to a group, often a profession, that can often be confusing or misunderstood.
Examples Examples Examples
FAQs Plug and play (electronics) Bait and switch (business)
AWOL (military) Cookies (computers) Value-added (business)
Mirandize (police) Teaser (newspaper) Firewall (computers)
Perp (police) Pick-six (sports/football) POTUS (political)

Other/Misc.: What follows is a list of words/phrases that should generally be avoided in academic essays. They tend to weaken the writing, or they are too casual or non-specific.
Avoid using: Instead, try these:
A lot There are numerous calls today at the office. Multiple individuals were late to work.
Really or very Instead of "really sorry." Say: contrite or remorseful. Instead of "very bad" --> heinous or dreadful
Stuff Too general/nonspecific. Say: Many characters had several issues (not "lots of stuff") they are exploring.
People Also too general. Say: When citizens (not "people") come together, anything is possible.
You, Your, etc. Usually not acceptable in academic writing. Avoid second person in most cases. Check with your instructor.
Nice Be more specific. Say: The weather outside today is certainly pleasant and sunny (not "nice").
Kind of/Sort of Again, be specific. Say: My brother was being mildly argumentative, but I ignored him.
Alright Nonstandard. Say: She was all right for now, but we were worried for her future. ("alright" = "all wrong") 
And/or, him/her, etc Avoid such expressions. Choose one. Say: This message, and its related attachments, are confidential. Same with pronouns-choose one. Say: It was up to him to decide the fate of the team.
Because of the fact that Say: Because of my poor driving record, I lost my license.
At the present time Say: Now I want to tell you all why I have called you here.
In spite of the fact that Say: Although I was angry earlier, I have since calmed down.
In the event that Say: If I am absent from the meeting, please take notes for me.
Are of the opinion that Say: We believe that your absence from the group has created problems.

These are just a few examples! Always seek to make your writing as clear and direct as possible.