Only

The adverb/adjective  only has an unfortunate tendency to wander aimlessly up and down sentences like a lonely  teenager wandering the school  corridors in the hope of finding  a friend.

Consider this:

I only drink coffee.
I drink only coffee
I drink coffee only. 

The writer wishes us to understand that she does not drink tea or other beverages. In the first sentence, however, she has misplaced the only because, like the lonely teenager, it desperately clings to the first thing it meets, which in this case is the verb drinks. 

This is wrong, because we might ask what is meant by "only drinking". Does it mean she only drinks coffee, but she does not inject it into her veins? She only drinks coffee, but does not eat it?

Clearly not. The second two sentences return the only to a safe position next to  coffee, which is where it belongs. They are therefore correct.

When we are in conversation we often use the construction shown in the first sentence. Again, we need to distinguish between what we say  and what we write.

Here are some more examples, with the wrong version on the left. 

I only have three friends--  I have only three friends
We were only able to eat one curry -- We were able to eat only one curry
I only asked because you wanted to tell me anyway - I asked only because you wanted to tell me ...
She only writes in purple ink - She writes in purple ink only/only in purple ink
They only want what's best for you - They want only what's best for you. 

As I say, when we are speaking, we allow the words to slip around in our sentences, and this is fine since the meaning is usually clear. In writing, it pays to be more precise.