Focusing adverbs point to a particular part of a clause.

Most common examples are: also, just, even, only, mainly, mostly, either, neither etc.

Position

As focusing adverbs point to a particular part of a sentence, the meaning conveyed often depends upon their position. It is best to place them in front of and next to the word or words modified by them.

Compare:

• Only John helped me to buy the house. (= Only John and no one else helped me.)
  
• John only helped me to buy the house. (= John helped me to buy the house, but didn't actually buy it for me.)
  

Exceptions

Too and as well are exceptions to this rule. They normally go in end position.

• She not only speaks English; she speaks French as well.
  
• He not only sings; he plays the piano too.