As with anybody getting a tattoo, check out the tattooist very carefully, not just hygiene wise but also the quaility of workmanship..
You need to inform the tattooist that you are diabetic,
The pain caused by tatooing can cause the blood sugar levels to drop, hence why a lot of non-diabetics feel faint or have the shakes while they are being tattooed..
You aren't allowed to eat or drink in the tattooing area, so bare this is mind you need to arrange regular breaks during the tattoo, so you can check BG, have a snack and also a prearrange signal with the tattooist so they can stop if you feel that you are going hypo..