You have a certain amount of freedom in deciding where to place yourmodifiers 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.
Misplaced Words
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