The purpose is to present your situation of needing advice and to allow the person with whom you are speaking make the decision whether or not they might be of assistance to you. Results from such contacts may include immediate telephone interviews, office visits, or rejections. Be prepared to meet requests by having a list of questions or your calendar near by to suggest a specific date for a visit. Follow up with a note of thanks and a list of details or your progress. It is common courtesy and smart sense to keep all contacts advised of your job status.
Some employers prefer a well-written letter of introduction.
Such a letter will specify that you are in the information-gathering process of your job search. It allows them time to consider the request and to fit a possible visit into their schedule. Such letters need to be concise and ask only for career information. Attaching a list of 5-10 questions will allow the person to flavor the type of information you want. It will also support the fact that you are seeking advice only.