Sliding scale is quite an old-fashioned way of dosing insulin, and can have much error unless one eats exactly the same way every day.
More modern approach is basal-bolus approach.
This is where basal (slow acting insulin) is adjusted to cover insulin requirements without food, and bolus (fast acting / meal time insulin) is dosed based on amounts of carbs and proteins that will be eaten at any meal.
The ratio of how much insulin to how much carb / protein is determined over time and with experimentation.
My Dr first told me to use 1 unit of fast acting insulin for 25 g of carbs, and adjust from there. Typically I will use 1 unit of insulin for 10 g of carbs in the early mornings, 1 unit of insulin for 20 g of carbs later in the day.
Hope this helps you find some direction.
Please come and ask more questions.