Preparation: The more structure and preparation you demonstrate to teh person you are interviewing, the better the interview will be.
The following are guidelines toward developing good interviews

Develop a statement of interest, including
What you find interesting about the subject
What you will be able to discover through the interview
that you could not otherwise research
Research thoroughly whatever public knowledge
you can find on the person, the project, the company, and/or events.
The interview begins before you meet the person!
Prioritize a set of objectives and questions
Going in prepared makes you look capable and competent
Discover what is necessary to fit into his/her environment/space;
ask advice of others if necessary.
Dress neatly and appropriately for the situation.
Your objective is to make the interview subject feel comfortable,
and willing to share what is important to them.
Ask yourself: "How would I want to be treated if the roles were reversed?"
Develop a checklist of what "tools" are needed in the interview:
notebook, pens, recording device, etc.
Arrange for the interview "on location" if possible and/or appropriate
It will add to its sense of place, voice, and story
Before the interview:

Arrive early
Avoid traffic, parking, getting lost problems
Silently observe where your subject works if possible the office environment, working conditions, co-workers and staff, how he/she is dressed, etc.
Don't be "nosey" but be alert!
Don't interfere with on-going operations
If you tape record the interview
Test your recorder, its tape and batteries before you start
Get permission, in writing or on the tape: sample form (.pdf)
While recording, continue to take notes, especially key points to be safe
Introductions (a "few" minutes)

Introduce yourself and your project
Ask for the person's name, title, business card,
photograph or digital image, company logo, etc. as appropriate
Try to make the person you interview
(and yourself!) comfortable. Some casual conversation is appropriate as ice-breaker: express your appreciation for their time and willingness.
Compliment their office, directions, your respect for their achievements, etc.
If this is your first interview,
share that you are developing your interviewing technique
If you know the person from before,
keep in mind that your project may require that you be impartial or neutral to that person's experience. Make no assumptions!
Offer a consent form sample form (.pdf)
Introductory questions
Be complimentary to set the tone
Demonstrate your interest and preparation
Verify a few known selected facts, sequences, etc.
(I read your biography and saw your degrees are in....
(The newspaper reported that your neighborhood has succeeded in...
(In your company's annual report, I read that the most successful product line is...
(What prepared you for your success in...
(How did you become interested in....)
(I read that you started out as a chemist, and developed yourself to become....
(What books or people most influenced your....
(I see that your position is responsible for....
(Who were your important role models or teachers for....
(What was the consequence of....)

The Interview

Treat the interview like a conversation with structure!
Begin with your list of questions
Follow chance openings
Keep in mind your objectives
Actively listen to understand and report
Affirm that you understand what they are saying
Do not agree or disagree with the person
Do not debate what they have to say
While taking notes,
don't hesitate to ask for clarifications or better understanding:
"Could you repeat that, please? I want to make sure I get all of that down."
"I am not sure I followed that, do you mean that...."

Know when to shut up
Listen carefully so that you know when to let your source pause to collect his or her thoughts. Don't feel the need to fill every empty space with conversation
Don't be afraid to say you don't understand,
or need more explanation.
Use your own words to repeat back; ask:
"So what you're saying is ..." or "So let me get this straight..."
Be willing at all times to be surprised; follow chance openings
Don't think you know what the story is about.
Don't let your own feelings or bias shape the questions you ask
Follow the order and priority of your questions

Transitions: be aware of time constraints and your purpose:
look for a convenient jumping off point to engage the subject
Develop more depth/complexity as the interview develops
given the comfort level and opportunity
Avoid yes/no questions
Ask some questions that can be only answered with a story
This reinforces your interest in not only getting "facts" but also the role your subject has played. It lends voice to the narrative, and can personalize the story for your readers.
Don't accuse (Why DID you ....?"),
rather ask if the person would like to respond to accusations,
or tell their side of a story, or...
Develop scenes and themes during the interview
(It sounds like .... is very important to you, what/how/... has it affected...
(What was most significant in....
(What difficulties or challenges were most important...
(How did you react to....
(How do you see your role in changing....
(At what point did you know you wanted to.... How did you meet this challenge or change?
(What do you see as your current/next challenge...
(In the ...., I read that you said ".........", can you provide more detail?
(How do you keep track of ....
(Some people say that ...., but you seem to take another path.
Can you explain the difference?)

Transition to conclusion

Keep aware of the time, and all the topics you need to cover
Ask if there are additional points that have not been addressed
Summarize a few important points to verify if you understand correctly
Ask for references for additional information,
sources for data, or advice for further development
Conclusion

Review your timeline toward completing your project
Volunteer to provide a copy
of your completed report, article, or a summary of the presentation,
including any reactions to the interviewee
Express sincere appreciation
Writing an interview essay:

Immediately after leaving the interview:
Organize your notes
Label and date notes and tapes for easy reference
Transcribe the audio recording, or important sequences and quotes
Set your notes aside for a day or two to get a fresh perspective
Re-read the assignment!
What specifically is the focus of the assignment?
Review the entire interview's notes and recording
Note from three to five major themes,
and compare these with the assignment's objectives
(You are now re-structuring the interview from its "narrative" sequence
to one of themes)
For each significant theme, find an appropriate quote
and cut and paste these into their categories
Follow the structure of any writing assignment
Refer to our guides on Writing Assignments
After completing the substance of the interview,
develop an introduction (remember your initial observations?) and conclusion.
Follow guidelines on
proofreading, verifying with and citing your source(s), and spell checking
If appropriate, with advice from your teacher,
send a copy to your interviewed subject with appreciation inviting feedback.
Types of interviews:

Celebrity and newsmaker
Understanding who stands behind success or notoriety
Professional profiles
Understanding professions, careers, companies, institutions
Project profiles
Developing a project history from inspiration (to conclusion) and consequences
Oral history
Learning about past events and experiences
Employment
Developing your interviewing skills will also help you when you are,
in turn, interviewed
Person-on-the-street interviews
Be brief and friendly, yet businesslike.
Don't walk up to people with a "sorry to bother you" attitude.
Develop a professional manner and act the part:

Identify yourself and explain what you're doing.
Request permission to ask a few questions
Ask for the person's name and where they're from:
Verify names -- especially spellings
Be brief and look for follow-up possibilities
Save tougher questions for near the end of the interview
Thank the person -- remember that anyone who consents to an interview is doing you a favor, whether they are getting anything out of it or not
If the story is being published,
let the person know where and what your name is again
No matter how rude someone is to you, be polite. Be businesslike.
Remind the person you've approached why you're there and, if you can, repeat your question. If the situation doesn't improve, walk away. And don't take it personally.