Agree with some of the others, the most important thing imho is to just take it slow, really, really slow. Almost forget about the story, and do story elements as you feel like doing them, try not to be all "type A" about reaching "the ending". This is a game to be enjoyed, and think of the story "ending" not as a reward, or a puzzle to be solved, but as something you'll reach someday after you've enjoyed all the game has to offer. Focus on exploring, studying the animals, learning to hunt, fish, take care of yourself, think of it more as going out for an evening ride after work on your horse to take in the sunset, and pick up a few herbs, maybe shoot a rabbit along the way. Just experience it and take it in. There is no hurry to "finish" this game. Most games have goals, you might want to acquire as much money as possible, or as much resources ... but in RDR2 I don't feel that is really the point.
There are a ton of technical tips about doing specific things that could be talked about, but my tip in general would just to be opportunistic - as someone above said, loot when you can, and always be aware of the things you need to progress in any category. There will be all kinds of objectives that you can have, but instead of working towards a specific one, my advice is to just enjoy the game and always have all of the next steps to your objectives in mind so that you can be opportunistic and take advantage of situations as they arise. Maybe you need a certain kind of animal to progress at something, or maybe there is a certain action you have to take to advance a skill, or a challenge to gain some resources, my advice is don't be so driven to "complete a project" and just have all of your projects in mind and enjoy finding pieces to the puzzles as you run across them.