At last, in response to a steadily diminishing number of requests (to steal a joke from my friend Paul Trigg, who probably stole it from someone else)–part 2!
Principal/principle
If you want an adjective, you want principal.
This post’s principal mission is to help people improve their English usage.
If you see principle used as an adjective, it’s wrong. Period. We’ll get to its correct usage in a minute.
Mnemonic: Principal has an “a” for “adjective.”
Principal as a noun means the owner of a business, the employer of an agent, the head of a school, a leading actor in a play, etc.–briefly, the most important person. The underlying meaning is the same as that of the adjective. (It also means the amount owed on a loan.)
The principal of the company worried that the principal on his loan was too high.
Principle means “a comprehensive and fundamental law, doctrine, or assumption.”
The principal strove to instill in his students the principles of mathematics.
If I think of a good mnemonic for that I’ll let you know.
Illusion/allusion and allude/elude
An illusion is a false appearance or idea.
She had the illusion that she understood the proper usage of “allusion.”
You might think of the “ill” in illusion as describing the results of suffering under one.
An allusion is a reference to another work, event, or idea.
Much of English literature contains allusions to the Bible and/or Shakespeare.
You might consider that “all” of literature contains allusions to other things. But that’s kind of stretching it.
Now for the verbs:
To allude, as you may have guessed, is to make an allusion.
Cyrano de Bergerac went ballistic when people alluded to the size of his nose.
To elude means to avoid or escape from.
No enemy could elude the point of Cyrano’s sword.
As far as I know, there is no verb that corresponds to illusion.
Imminent/immanent/eminent
Imminent means “about to happen in the very near future.”
She feared the death of the English language as she knew it was imminent.
Immanent is a technical philosophical/theological term meaning “inherent,” or “remaining or operating within a domain of reality or realm of discourse.”
God is immanent within His creation.
Eminent means “prominent” or “conspicuous.”
The eminent scholar hoped his Nobel prize was imminent.
Except/accept
Except is a preposition meaning “other than”; accept is a verb meaning “receive” or “agree to.”
She could not accept the idea that no one except herself understood what she was talking about.
Prescribe/proscribe/subscribe
Prescribe means to lay down a rule or to write a medical prescription.
The doctor prescribed lime, coconut, and two aspirins for the patient’s bellyache.
Proscribe has almost exactly the opposite meaning: to forbid.
Overindulgence in carbohydrates is proscribed for patients suffering from diabetes.
Subscribe means to enroll one’s name (literally or figuratively) in a list of those who agree to a proposition, receive a magazine regularly, etc.
I cannot subscribe to the idea that grammar does not matter.
If the requests diminish far enough, part 3 may be imminent–unless it is proscribed by your comments.
The Wayfaring Writer 
Oh, I would never dream of proscribing any post of yours.
And if you really want to, you may observe a covert Mr. Darcy reference. But you don’t have to. I almost didn’t.