Carbohydrate counting
Since carbohydrates raise blood glucose the most directly, many people on mealtime insulin count grams of carbohydrate per meal and use a personalized insulin-to-carb ratio (set by their care team) to calculate a dose.
Protein, fat, and glycemic index
Protein and fat affect blood glucose more slowly and less directly than carbohydrates, but large amounts of either can still raise the total insulin needed for a meal and delay when the effect shows up. The glycemic index of a carbohydrate source (how quickly it raises blood sugar) also affects how a dose should be timed.
Meal timing
Taking rapid-acting insulin at the right interval before eating (rather than after) generally leads to smoother post-meal glucose control, since it gives the insulin time to start working before glucose from food arrives.
General eating patterns
There's no single "diabetes diet" required to use insulin, but many people find that consistent meal timing, attention to portion sizes, and a diet emphasizing whole foods, fiber, and balanced macronutrients makes doses easier to predict. A registered dietitian familiar with diabetes can build a plan specific to your goals.