This is a question with many answers, as everyone has their preferred way of stacking an ID.
Seige has a point, however my stack contradicts his version to an extent.
My Top and bottom cards on one side is an ace, and on the other side a Queen. I won’t go into more detail here, just incase i get told of for revealing more than I should.

If anyone would like to know how mine is stacked, don’t hesitate to PM me.
I use the ID in nearly all my performances, and have done for the past 10 years. I have found that the best stack, is the one that helps you remember were all the cards are located. Also you are nearly always performing the ID to Lay People, so no matter what card is at the top, they will not consider it suspicious. Maybe I am wrong with this assumption, but it works for me.