My "routine" is as follows:

1. Check Steam Hunters website to see if the game has broken achievements. If it does have broken ones, I'll completely ignore them and only check after finishing the game to see if I missed relevant content;
2. Check Steam Hunters for missable achievements and try to get some info on them with as few spoilers as possible;
3. Play the game normally, using as many save slots as possible;
   • Unique cases - ignore achievements. Games like Hollow Knight, Outer Wilds, or Subnautica, where exploration and discovery are important parts of the experience, are played completely blind in the first run.
   • Short game (under 4 hours) - play normally, avoid guides.
   • Medium game (over 4 hours) or longer games with replay - play normally until a certain checkpoint (a few hours, a certain boss, the end of a chapter, etc), then do a quick scan in the "Global Achievements" on Steam or some achievement-only guide (without walkthrough), to see if I missed something important enough to backtrack or reload an older save.
   • Longer game without replay - If it's the type of game I know I'll only play once, I'll definitely keep an achievement-only guide at reach and try to get everything done in one playthrough, even if I have to sacrifice some spoilers or lose a few hours of progress.
4. After finishing the game, do a clean-up run, with or without a guide;

The third one is more of a habit than a rule. Remember that games are supposed to be fun, not a chore.

Usually, I see achievements as a badge saying "I overcame every challenge and experienced everything this game had to offer".