IAAD, type I, though. Spent a couple years as type II.
The very short form of a good diabetic diet is: Divide the plate into half. Divide one half in half so you’ve got a half and two quarters. Put vegetables on the half, starch in one quarter, meat in one quarter. He can eat at MacDonalds so long as he gets a large salad and only one hamburger.
Scale this up if he’s a big eater, but bear in mind that the more he eats, the harder it will be to maintain control. Not impossible, just more difficult.
Find some exercise he can do several times a week if he’s not already exercising. I started out walking for an hour, several days a week, then started doing stairmaster & weight training, then got into karate and kendo classes. Ironically enough, aside from the diabetes, I’m in the best shape of my life (I’m 40).
Once he’s gotten the instructions on testing his blood sugars, he needs to test fairly often until he learns how his body feels at various levels, and then retest every once in a while to make sure he’s remembering the feelings right.
As much as possible, you (he) should cook, rather than eating out. Unless you are VERY careful, eating out (or even cooking packaged meals) is not as healthy as assembling meals from your own ingredients, where you have much better control over how much sugar goes into the food.
Something I figured out on my own: keep an eye on anything they make bread, oil, sugar, or booze out of. They’re all pure carbos and/or fat.