What does "only" mean? I understand the technical and logical distinction between "if" and "only if" and "if and only if".  But I have always been troubled by the phrase "only if" even though I am able to parse and interpret it.  Also in my posts on this and other sites I have frequently had to make edits to migrate the term "only", sometimes across multiple structural boundaries of a sentence, which is empirical evidence to myself that I don't intuitively know the meaning of the word. 
Is there any simple rule that I can use to determine whether or not it is appropriate to use this word in a particular context in order to achieve more clarity?  In mathematical discourse, what are some other common lexical contexts, meaningful or not, in which appears the word "only"?  Why do I often write "only" in the wrong place?

Here are some links from other websites which helped me:
1.http://courses.umass.edu/phil110-gmh/text/c04_3-99.pdf
2. https://english.stackexchange.com/questions/32343/if-vs-only-if-vs-if-and-only-if
3. http://aristotle.tamu.edu/~rasmith/Courses/Logic/Exercises/1.3.extra.pdf‎
4. http://forums.philosophyforums.com/threads/only-if-vs-if-and-only-if-27842.html
