One strength of the English language its flexibility. We have lots of ways of rewording things. For example, we can use simple past tense (I went to the store), or we can use a two-word “paraphrastic” past tense, usually for emphasis or negation these days (I did go to the store, or I didn’t go to the store.).
Notice, though, that in English, when we use a paraphrastic tense, only ONE verb carries the tense: “I did go to the store,” not “I did went to the store” (or, to get crazy with it, “I did wanted went to the store.”). Naturally, in forming past tense questions, we also split the past marker off: “Did you go to the store?” not “Did you went to the store?”
That’s very, very simple and straightforward, right?
Of course not! Ha! Ridiculous! This is English. How can it be simple?
What happens when you introduce another type of paraphrastic in there? Specifically, I’ve come across this issue more than once with the verb phrase “used to.” Obviously, in simple past, we can say, “I used to go to the store.” (And equally obviously, never “I used to went to the store.”)
“Used to” is already extra tricky because vocally (where you’d usually hear this colloquialism), “used to” and “use to” are pronounced almost identically, so many speakers aren’t sure what the correct form is in the first place. (It’s “used to.”)
But what happens when we get crazy with the paraphrastic past, emphatic or negative?
“I did use to have a job, you know.” vs. “I did used to have a job, you know.”
“I didn’t use to worry about these things.” vs. “I didn’t used to worry about these things.”
“Did you use to visit often?” vs. “Did you used to visit often?”
While “use to” often looks wrong in this context because the simple form is correctly “used to,” I’m of the opinion that you shouldn’t have two tense markers in the same verb. Just like you wouldn’t say “I did/didn’t went to the store,” I don’t think you should say “I did/didn’t used to go to the store.”
And of course, in very formal writing, you should never have used either 😉 .
Want to get technical? Of course! Here’s a usage note on “used to” from the Oxford American Dictionary to back up my theory (emphasis original):
1 The construction used to is standard, but difficulties arise with the formation of negatives and questions. Traditionally, used to behaves as a modal verb, so that questions and negatives are formed without the auxiliary verb do, as in it used not to be like that and used she to come here? In modern English, this question form is now regarded as very formal or awkwardly old-fashioned, and the use with do is broadly accepted as standard, as in did she use to come here? Negative constructions with do, on the other hand (as in it didn’t use to be like that), although common, are informal and are not generally accepted.
2 There is sometimes confusion over whether to use the form used to or use to, which has arisen largely because the pronunciation is the same in both cases. Except in negatives and questions, the correct form is used to: we used to go to the movies all the time (not we use to go to the movies). However, in negatives and questions using the auxiliary verb do, the correct form is use to, because the form of the verb required is the infinitive: I didn’t use to like mushrooms (not I didn’t used to like mushrooms). See also utilize (usage).
And, of course, for the negative, you could always rephrase with “never” (if that’s what you mean).
What do you think? Did you use to think that? 😉
Photo by Miguel Ángel Díaz Rey via Flickr & CC license
Thee problem is this: there’s only a handful of words in the English language to express those actions: smile, beam, grin, smirk, simper. Nodding is even worse: nod. Other versions of this one tend to draw attention to the words instead of showing the characters’ actions: bobbed his head (“up and down,” if you want to make it even more annoying). 
And do they need the forbidden modifier? I think so. Can you infer the meaning of his grin with just “He smiled at her”? (I have two images in mind here: “He smiled at her. Mmm. Lunch.” and “He smiled at her. Oh, a friend.”) A thumb chewer may be a small child seeking comfort, an adult pondering a problem or a guy with a nervous habit.
Contrary to popular thought, not all action verbs are strong verbs. In the sentence “Ali walked down the road,” “walked” is an action verb. It is also a generic verb. It tells us that Ali is using her feet to advance across a surface and nothing else. 
Consider this sentence: “Sari’s words caused Anthony great confusion.” The sentence is grammatically correct. Moreover, its meaning is clear. But how much more vivid and exact is the revised sentence “Sari’s words confused Anthony”? Or even better, “Sari’s words baffled Anthony.” 
That is, until I got about four lines into page one. The book was a mess from start to finish. Even though I read the thing about a dozen years ago, I could still rant for days on the all the problems in the book (let’s just say this guy didn’t have the first clue about how to put together a coherent story, let alone a coherent sentence).
For example, don’t do this: “These flowers are for you,” he smiled. 