You have a certain amount of freedom in deciding where to place your modifiers in a sentence:
We rowed the boat vigorously.
We vigorously rowed the boat.
Vigorously we rowed the boat.
However, you must be careful to avoid misplaced modifiers -- modifiers that are positioned so that they appear to modify the wrong thing.
In fact, you can improve your writing quite a bit by paying attention to basic problems like misplaced modifiers and dangling modifiers.
In general, you should place single-word modifiers near the word or words they modify, especially when a reader might think that they modify something different in the sentence. Consider the following sentence:
[WRONG] After our conversation lessons, we could understand the Spanish spoken by our visitors from Madrid easily.
Do we understand the Spanish easily, or do the visitors speak it easily? This revision eliminates the confusion:
[RIGHT] We could easily understand the Spanish spoken by our visitors from Madrid.
It is particularly important to be careful about where you put limiting modifiers. These are words like "almost," "hardly," "nearly," "just," "only," "merely," and so on. Many writers regularly misplace these modifiers. You can accidentally change the entire meaning of a sentence if you place these modifiers next to the wrong word:
[WRONG] Randy has nearly annoyed every professor he has had. (he hasn't "nearly annoyed" them)
[WRONG] We almost ate all of the Thanksgiving turkey. (we didn't "almost eat" it)
[RIGHT] Randy has annoyed nearly every professor he has had.
[RIGHT] We ate almost all of the Thanksgiving turkey.
Misplaced Phrases and Clauses
It is important that you place the modifying phrase or clause as close as possible to the word or words it modifies:
[WRONG] By accident, he poked the little girl with his finger in the eye.
[WRONG] I heard that my roommate intended to throw a surprise party for me while I was outside her bedroom window.
[WRONG] After the wedding, Ian told us at his stag party that he would start behaving like a responsible adult.
[RIGHT] By accident, he poked the little girl in the eye with his finger.
[RIGHT] While I was outside her bedroom window, I heard that my roommate intended to throw a surprise party for me.
[RIGHT] Ian told us at his stag party that he would start behaving like a responsible adult after the wedding.
A squinting modifier is an ambiguously placed modifier that can modify either the word before it or the word after it. In other words, it is "squinting" in both directions at the same time:
[WRONG] Defining your terms clearly strengthens your argument. (does defining "clearly strengthen" or does "defining clearly" strengthen?)
[RIGHT] Defining your terms will clearly strengthen your argument. OR A clear definition of your terms strengthens your argument.
The infinitive form of the verb consists of the word "to" followed by the base form of the verb: "to be," "to serve," "to chop," etc. Inserting a word or words between the "to" and the verb of an infinitive creates what is known as a split infinitive. Prescriptive grammarians, who knew Latin grammar better than English, once decreed that a split infinitive was an error, but now it is growing increasingly acceptable even in formal writing. Nevertheless, some careful writers still prefer to avoid splitting infinitives altogether.
In general, you should avoid placing long, disruptive modifiers between the "to" and the verb of an infinitive. However, you must use your judgement when it comes to single-word modifiers. Sometimes a sentence becomes awkward if a single-word modifier is placed anywhere but between the elements of the infinitive:
[WRONG] The marketing team voted to, before they launched the new software, run an anticipatory ad campaign. (disruptive -- the infinitive should not be split)
[RIGHT] The marketing team voted to run an anticipatory ad campaign before they launched the new software.
The dangling modifier, a persistent and frequent grammatical problem in writing, is often (though not always) located at the beginning of a sentence. A dangling modifier is usually a phrase or an elliptical clause -- a dependent clause whose subject and verb are implied rather than expressed -- that functions as an adjective but does not modify any specific word in the sentence, or (worse) modifies the wrong word. Consider the following example:
Raised in Nova Scotia, it is natural to miss the smell of the sea.
The introductory phrase in the above sentence looks as if it is meant to modify a person or persons, but no one is mentioned in the sentence. Such introductory adjective phrases, because of their position, automatically modify the first noun or pronoun that follows the phrase -- in this case, "it." The connection in this case is illogical because "it" was not raised in Nova Scotia. You could revise the sentence in a number of ways:
For a person raised in Nova Scotia, it is natural to miss the smell of the sea. (the phrase no longer functions as an adjective)
Raised in Nova Scotia, I often miss the smell of the sea. (the phrase functions as an adjective but now automatically modifies "I," a logical connection)
A dangling modifier can also appear when you place an elliptical clause improperly:
Although nearly finished, we left the play early because we were worried about our sick cat.
The way this sentence is structured, the clause "Although nearly finished" illogically modifies "we," the pronoun directly following the clause. An easy way to rectify the problem is to re-insert the subject and verb that are understood in the elliptical clause:
Although the play was nearly finished, we left early because we were worried about our sick cat.