Suggestions on the best way to study for the promotion board with new ADP?

I would start by reading FM 7-22.7, followed by ADP 6-22 and then ADRP  6-22. Then start with ADP 1-0, and work though them in order. ADPs are designed to be ~10 pages of actual information; easily digestible. Pay attention as you read to the table of contents of each ADP, usually I try and glean the concept of each manual (basic principles etc) before, during, and after each ADP. Becoming a Conceptual thinker now will make understanding and interpreting doctrine much easier as you move up.

I would suggest two hours a day. Hit the stuff you know you don't know first.

Think of the ADPs and ADRPs of being similar to "Cliff Notes" like in high school or college.

They're a lot easier to read and understand compared to some FMs. I recently went to the promotion board and prior to going I downloaded the ADPs/ADRPs on my MOI and some that were not and I read them. You want to make sure you not only read the material but also pay attention to the charts (i.e. Institutional/Operational/Self Development Training in ADP 6-22)

Hope this helps! Good luck!