The best way to reach me is by email (not facebook). My address is:
Although I do my best to respond to as much as I can, I admit that I am not able to respond to everything. (Also, my replies are often terse. Please don't be offended if so; I am just trying to be efficient.)
In some cases your question may already be answered on the site: e.g. tutoring, contest resource recommendations or the FAQ. If you need help with an olympiad problem, you are better off asking on a forum like AOPS. Contrary to popular belief I can't sight-solve everything!
Here are some hints:
Comments, thanks, or suggestions on my writing are always appreciated! This includes any typos you find, no matter how trivial.
Specific queries get faster and better responses. So "can you explain this line of your solution to USAMO 20XY/Z?" will usually be answered pretty swiftly. Conversely, "how do i geo" will get at best a link to the FAQ.
Proper syntax, English, capitalization, etc is appreciated. (I know some of you are not native English speakers, so I try to overlook this when I can.)
Please be patient. "Bumping" a message before I have found time to respond is likely to annoy me. I will not respond to a non-urgent message that is bumped after less than one day.
Don't be too shy! I might sound scary here, but if you have a good reason for contacting me and do so politely, then I won't mind. I am happy to help where I can.
(Examples of good requests: specific math query, something I wrote is unclear, found a typo, follow-up questions, permission requests, questions on my past experiences, etc. I'm sure there's more.)
In particular, there's no need to send an email asking if you can ask a question.