One of the things I often see done poorly in writing is the overuse of time and sequence words, in particular 'before' and 'then'.
One of the things a writer needs to bear in mind is that, as with software, there are defaults in writing, and just as when interacting with software it is never necessary to specify default values, so it is when we write.
MISUSE OF 'THEN'
If not the most common, one of the most common defaults is that of sequence. In a long sentence which describes several actions, the default is that the reader will understand the actions to have taken place in the order in which they are mentioned.
E.G. - Rover pounced on the rat, pinning it to the ground, and bit off its head.
See how, when you read this sentence, you automatically envisage the pouncing, pinning and biting in that order? Now, consider how it might have been written (and often is, sadly).
Rover pounced on the rat, pinning it to the ground, then bit off its head.
Now, I don't know about you, but to me that looks clunky. And you've just broken one of the most fundamental rules of fiction - show, not tell. The sentence already shows the reader the actions that are happening, and the order in which they are taking place - but with the addition of 'then', you have also told the reader this. That is like
"Hello, Mother." I said hello to my mother.
And that's just plain wrong. Right?
So. Don't use 'then' unless it is going to add something to your sentence.
Now, there may seem to be exceptions to this, because occasionally it may be used for emphasis. Consider the following:
1. She picked it up, toying with the idea of reading it, then shoved it back in the drawer.
This sentence, if you remove 'then', will read:
2. She picked it up, toying with the idea of reading it, and shoved it back in the drawer.
Do you see the difference? In the first example, there's a sort of pause at the 'then' - it reinforces the idea of a moment of decision. In the second example, that is lost, and we have a mere string of actions. The first sentence is better, and that is because the 'then' in this case did add something to the sentence - it added emphasis to the break between the picking up and thinking about reading and the subsequent decision to put it back instead.
This, then, is not an exception to the rule, because in this case the word did have its contribution to make.
MISUSE OF 'BEFORE'
As well as 'then', 'before' often marks a failure to recognise built-in defaults.
EG: Rover pounced on the rat and pinned it to the ground before biting off its head.
This is just nasty. We know it's before, because it's before in the sentence. To show things happening in another order, you'd have to do something else - hopefully the common-sense option of just putting them in the other order in the sentence. And yet I see this a lot in the work of novice writers. Don't do it. Just don't.
An even more egregious misuse of 'before' occurs when, for some demented reason, the writer depicts actions out of their sequence.
EG: Before biting off the rat's head, Rover pounced on it and pinned it to the ground.
There may be some instances where it is genuinely useful to show actions outside their time sequence. This, however, is not one of them, and neither are most of the instances where I see this sentence construction. Aside from being rather silly, this also has a great drawback, especially in longer, more complex sentences. With this construction, the reader must hold the first bit in his mind while he reads the rest of the sentence, and then shuffle everything into place. Of course this will happen below the conscious level (unless he is a very poor reader), but it still must happen, and the result is that you are asking your reader to do extra work, adding to any fatigue he may be experiencing. If you keep this up throughout your work, these tiny increments of reader fatigue will start to accumulate, and if you do it enough, some readers may put down the book. That is never what you want. The more difficult it is for the reader to stop reading, the more positively he is going to view your work. Have you ever seen a review where anyone said, "I stayed up all night to finish this. It is the worst book I've ever read." Well, have you? No, you have not, and you never will. The single most important thing in making a reader love your work is to keep him turning the pages.
THE GOLDEN RULE
As with so many fields of endeavour, the golden rule is 'Keep It Simple'. Don't be contorting your sentences into uncomfortable shapes. Keep it straightforward. Many great writers have done so before you.