There are 2 ratios that are so important for a diabetic on insulin. The first is the insulin to carb ratio (I:C). This is how much insulin you take for a certain amount of carb. Do you carb count? Most folks start at 1 unit of fast acting insulin for every 15 rams of carb. Eat a known amount (read the label) and then test 2 hours later. If you are high or low you will know which way to change. Some folks take 1:5, I took 1:25. Everyone is different.
The other you want to know is your insulin sensitivity factor. This is how many points one unit of insulin will drop your glucose. Mine was 1:80. Many folks are much less. Again, take some insulin when you are high and test and see how much you come down. Don't forget that the higher your glucose, proportionally you may need more insulin as you become more insulin resistant when you are higher.
Hope this helps a bit. You need to know these things to properly take care of yourself. The doc can't do it on a day to day basis. Only you can - but the good news is that with the proper knowledge you can get excellent control.
Cora