OK, so there aren't any "official" rules to diabetes, there are some very broad and general guidelines and there is a very good reason for this. It's because everybody is different and everybody's diabetes is different so too are the guidelines for each person.
So here are the rules I have come up with for myself, which are specific to when I'm having a bad day with Type 1 diabetes:
Always take your insulin.
No matter how you feel now, you will feel a thousand times worse if you don't take your insulin. Remember how ill you felt just before you were diagnosed. Yeah, that feeling will come back if you don't take your insulin.
Test your blood sugars regularly.
Now that you are taking your insulin like you should, it's time to look at how much you are taking. The best way to determine if you're taking sufficient amounts is to do some reconnaissance blood sugar testing.
To check if you are taking the correct insulin dose for your meals and snacks, test your blood sugars before you eat and then again two hours after. If you want to check on how much basal insulin your body needs get some advise from your diabetes team. If they don't have enough advice for you, you can do some research on websites such as Diabetes Health or this website.
Use some form of carbohydrate counting.
There is quite a bit about diabetes management that you just cannot control or even measure, such as hormones, stress, illness. However, there are three elements of diabetes management that you can control and measure. They are insulin, food, and physical activity. If you know the quantities of insulin, food and physical activity then you can come up with some sort of system to work out how many grams of carbohydrate will be covered in a unit of insulin. My carb counting involves reading nutritional labels and weighting out the carbs.
And there you have it! Those three rules are my biggy's. Even if I'm feeling a little burnt out I make sure I don't waiver on these three rules for myself. I feel like if I just keep to my three "biggies" that I can keep from drowning in the diabetes doldrums and keep complications at bay.
After that, if I'm feeling a bit more positive, I troll through the many reliable diabetes websites and support forums for new information or a new way of saying something old that makes more sense. I also have my real life support group of people with type 1 diabetes who never fail to give me a kick-start. :-)