The biggest regret that I hear about PD in schools is that they are too frequently perceived as either disconnected and out of context or used poorly for the distribution of logistical information that could otherwise be communicated via email or notes left in teacher mailboxes. Every school should have a theme to their PD narrative. PD should be thought of as an on-going, responsive conversation about teaching set in context of the needs of students in your school. The methods of PD should seek to replicate the models of promising practice, and they should be designed with a global focus on equity. That is, the meta-consideration of What equity questions are we asking about our policies and practices? should be interwoven within the discussion and modeling of promising pedagogical strategies.
I'd also recommend adding Lampert's Problems of Practice (PoP's) Model into the equation. Lambert's PoP's help to clarify where in the practice environment specific supports are directed. Short-circuits anywhere in the paradigm can undermine student outcomes and are especially impactful for your most vulnerable students.