Here’s something I see a lot in other people’s writing, and I know I sometimes make this mistake myself.
Where you place the word “only” in a sentence can transform the sentence’s meaning. For example, consider the meaning of each of the following sentences:
#1: I only drink beer on Friday nights.
#2: I drink only beer on Friday nights.
#3: I drink beer only on Friday nights.
The first sentence (I only drink beer on Friday nights) means that on Friday nights, I do nothing but drink beer. No shooting pool at a biker bar, no catching up on the Guiding Light episodes I’ve taped during the week. Nope, the only thing I do on Friday nights is drink beer.
The second sentence (I drink only beer on Friday nights) means that on Friday nights, the only thing I drink is beer. The “two-buck Chuck” remains in the fridge because on Friday nights, I swear off the wine; the only thing I drink is beer.
The third sentence (I drink beer only on Friday nights) means the only time I drink beer is on Friday nights. If my intention is to express that I have exercise enough self-control to limit my beer consumption to one blessed night per week, this is the sentence that reflects my intention accurately. (And for once in my life, I’d be writing fiction.)
You get it, right?
Just remember: the best rule in regard to the word “only” is to place it immediately before the word or phrase it modifies or limits.