If you are okay with this, you should shave your head before the first session takes place.
There are a few reasons to achieve this: The shock after the first session will be lessened. You can find all marks and scars, which you may decide to leave or cover with the treatment.
If you suffer from dry skin, this will give you the opportunity to moisturize properly before you undergo treatment.
If you are tanned, you can give your scalp some time to balance out the colours.
The most important thing to consider is moisturising, as you will need to do this at least 3-4 times a day in the final days leading to your treatment.
You should not be worried about the particular moisturiser you use, you just make sure that you give your technician a healthy canvas to work on, without any dry spots to impede the process.
If you wish to use painkillers, you should start making the choice of what to use as early on as possible or otherwise you may forget about it.
Do not be overly concerned however, as scalp micropigmentation treatments only usually involve mild discomfort that is perfectly manageable.