This seems to keep coming up on the boards.
Your CDE or Endo should have (be giving) you a scale to help get you started on this. One unit per X grams of carbs, and one unit per number of units needed to bring down a high BG.
I hope they are helping you because you really need a starting point and then a way to analyze your results.
There are diagrams and charts and formulas they use to figure this out, so hopefully they will work with you on this.
I know no one would encourage you to do this without help until you have been doing it for a little while, then you make your own changes.