I enjoy helping people explore the cultures of various English speaking countries. There are a lot of interesting aspects to English speaking cultures that I get a kick out of sharing with people. I am a fan of movies, plays, literature and music. Sharing and helping people understand these aspect of English if very rewarding for me.
I moved to Sapporo, Japan in 2006. I had been an English teacher and a U.S. Citizenship Test tutor before that. I had also taught kids reading and photography so going into English teaching was a natural option for me.
The reasons I hear most often are travel, job or educational opportunities and to help with testing here in Japan. My favorite answer was just given to me recently from a middle school student. She wanted to be able to understand the world better by finding English news sources to compare and contrast with the news sources here in Japan. Very mature answer.
That depends on which language(s) you have experience in. If you are coming from an Asian language, it will be more difficult than if you are coming from a western European language. It is definitely not easy though. Spelling, different pronunciations for the same letter combinations (ough), exceptions to almost all rules, so many words for the same ideas, such as - fantastic, terrific, amazing, wonderful, awesome. English is very idiosyncratic. That is also one of the most interesting things about English.
American English could be considered more casual. The "flap-t" in words like forty (4-D), kettle (ke dil) take some getting used to as well. It is also very creative and allows for a lot of self-expression through idioms and slang.
Sports, particularly baseball, movies and music would be the top 3.