The Department of Ecology is charged with writing regulations under SEPA.
The Department's website provides an Open Rulemaking page that lists proposals in various stages of the rulemaking process. Look under "State Environmental Policy Act (SEPA) for the status of relevant proposals.
The SEPA Handbook provides vital guidance on the SEPA process (PDF).
The Department of Ecology has created a couple of guidance documents that are intended to assist both proposal applicants and interested citizens: