There is no simple answer for this question, except to say that Acupuncture is a powerful 'medicine', or tool to produce states of health in the mind-body-spirit realms. It is old, dating back to over 3000 -5000 years. This in unimportant except to note that something so very primordial in nature, is still in existence and endorsed by WHO (World Health Organization) for 600 plus disharmonies of the physical-mental states of man. Several styles of Acupuncture are in current use. It is not unusual to find an Acupuncturist that prefers one discipline over another. It is important to find someone that has expertise in whatever you are seeking help with. Some basic data collection will help guide you to the correct Acupuncturist for yourself. I suggest 'prayer' to help find the person you seek, AND be prepared to do a little homework.
Always ask for the number of Years of education of formal study in Acupuncture, and how long treating.  4-6  years of study is becoming the standard for Acupuncture/Herbology.However, with it's origins based in Taoism there is always the possibility that the Acupuncturist will have 'insight' to help you regardless of length of formal training,or style being used. ' Seek with correct action, motivation, and ye shall find.' 
A history/physical will be obtained before treatment begins. The data the Acupuncturist collects to treat could include tongue/pulse diagnosis as well as other items the patient brings to the treatment. Intake on a first treatment may range from 20 minutes- 1 hour. Rarely will a 2 hour intake be necessary. Treatment time on the table will consist of 20-30 minutes after needle insertion.
As a system of medicine AP uses natural laws and energetic principles with an application of needles, energy, and pressure on points that may have oils applied to them. Each point provides a 'specific function' in body, mind, or spirit, that allows for free flow of vital energy for health and well being.  Gates, windows, sky points, earth points as well as wood, fire, water, and metal points are tapped and used to direct 'flow' of what has become known as 'qi'.
Acupuncturist needles are gently placed at these points with a specific 'intent' of balance, and harmony.  A sensation of warmth, tingling, numbness are normally felt. Most people are surprised at the depth of relaxation, the intensity of the energy that occurs, and the sense of 'well being' that occurs during treatment.  Often relief from symptoms is felt immediately. The patient often finds themselves looking forward to their treatment. Acupuncture has been found to be highly effective not only as a 'preventative' medicine, but as a drug free treatment to produce states of well being that often require the use of medicinals. From a western perspective acupuncture has shown to release 'endorphins' from the brain which make acupuncture particularly effective in pain control.
When I treat my patients I often make sure that the patient is given what they need. I will often treat a physical injury and stay at the body level. At other times I find it necessary, and therapeutic to engage the patient at the mind-body-spirit level. I do not make light of this type of treatment, and will make sure the patient is in an 'aware' state of being. This type of treatment is a special gift, and not one that is routine.  It is an art to be able to help other's at this level, and few acupuncturist understand this style of treatment.  The five element Acupuncturist understands this best, however 'intent' of the acupuncturist is again the most important factor. Someone that was trained in an 8 principle style may be able to manipulate the energy of the patient to the best effect for a complete healing. It is important to do some research, and then proceed with some history of the Acupuncturist.
Best wishes for a wonderful treatment!
God Bless,
James