Understand the basics pp 2-27 to 2-40 of the RAI Manual
Continue on to Chapter 6
Review the Medicare Benefit Policy Manual
http://www.cms.hhs.gov/manuals/Downloads/bp102c08.pdf
Attend Medicare training seminars provided by your Fiscal Intermediary. Keep their website in your favorites. There are valuable tools available in there.
Join a discussion group (free) to get assistance in pursuing a simple to complicated scenario. Post questions here. Seasoned MDS/PPS coordinators lurk the forum often.
A free downloadable PPS calculator to determine ARDs, grace days, payment period, physician cert/recertification, etc will be a convenient tool to have. Getting PPS assessments done on time is a top priority. Start honing your dynamic and persuasive traits. Befriend the Rehab therapists since they will play a major role in determining the best ARD to maximize your RUGs.
Knowing MDS is learning to ride a bicycle. Since you have that skill, learning the PPS is simply steering the bike w/ one hand.
Good luck!