Honestly, if you are starting from zero now preparation now, I wouldn't bother. You are going to need notarisation and police records from your home country, documents and tax returns from your HR, plus time to have the PR desk check them all, vet them. You normally have to get the ball rolling well before the offical announcement.
Given you are married to a Thai citizen you can skip PR anyway for roughly the same qualifications. Paperwork is much easier and it only costs 5,000 baht (vs 98,000 for PR). You can apply all year around too. No need to choose nationalities and the Thai language test is waived for married applicants.
https://www.thaicitizenship.com/thai-citizenship-application-process/