• Establish your target range for blood sugar levels. Common upper limit is 140 mg/dl = 7.8 mmol/l. Commit to keeping your blood sugar under this level at all times. As you gain better control, you may want to lower this limit by several points.
• Test right before eating. Log the reading.
• Test again one hour after your first bite, and log the reading along with what and how much you ate. For most people, this is assumed to be roughly the peak - the spike - from the meal.
• Test a third time two hours after your first bite. The purpose of this test is to show your blood sugar dropping back to about what it was before the meal. If it is, you're showing a good second phase insulin response. If it is not, you should continue testing until you find your blood sugar beginning to drop.
Analyzing these readings along with the foods you've eaten enables you to see which foods have the worst effect on your blood sugar, so you can avoid consuming them in the future.
It is fair to give each meal a second chance, in case there could be outside influences on the elevated reading, but after two or three experiments, it is wise to avoid or sharply restrict the foods which drastically spike your blood sugar. After several weeks of extensive testing this way, you'll have compiled a personalized list of foods you can eat safely, for the most part.
Not saying things don't change, and foods which were safe at one time could become troublesome later, but in the general scheme of things, eating to your meter is an excellent way to hold diabetes in check.
This can also be used to test individual foods such as fruits and things you suspect are going to spike you, but you'd like to know if perhaps you can eat small amounts.