If you haven't already scanned it, wait 24 hours, then start it.
Some of us find we get erratic readings those first few hours while our body adjusts.
If you have started it, don't worry just note the first 24 hours but don't get alarmed if readings seem either high or low, just confirm them with a finger prick.
Then it's up to you, eating low carb may prove to you that your ng is hardly affected, or eat high carrn and see just how high your bg goes.
You might want to test foods you are really missing to see if you can tolerate them.
But in any case remember several other things such as stress or exercise can also affect g so test individual foods more than once to get an overall picture.
There's no hard and fast rules, it's a tool for you to use. Very informative but don't let it become obsessive.
Let us know how it goes