OP here. Starting point from my own scramble: begin gathering documents MONTHS before expiry, because you often need fresh proof-of-address, income and continuous-residence evidence, and some of those take weeks to obtain. Leaving it to the last month is how people fall out of status.
My first permit expires in a few months and the renewal feels almost as daunting as the original application — different documents, proof I've actually been living here, and horror stories about leaving it too late and falling out of status. When did you start your first renewal, and what caught you off guard?