I am a marketing researcher. I have the following question on primary
data collection methods: for three of the questioning methods: focus
group, personal interviews, and survey (mail or phone), is there a
guideline on the length (and content) of each of these methods? for
example, how long is usually a mail survey or a phone survey? 5 pages?
1 hour? To get good results using the three methods, I would like to
know the research practice or guideline for the length and content of
these methods.

Check out these websites:

http://whyfiles.org/009poll/

http://www.ropercenter.uconn.edu/pom/polling101.html

Good luck!