I've seen a lot of lists of tips and while some are key, I thought I would do my own because even watching videos of 50 tips for RDR2, they still didn't touch on things I would have.
Constantly bond with your horse - this one is discussed in many, but it is pretty key. Click in the left thumbstick about every 5 seconds as you ride around to praise your horse. This will easily increase your bond with him. Feeding him does as well. At twenty five cents a shot, hay is the best meal per bang for your buck for your horse. Wild carrots are a close second since they are free, you just have to find them. And last, don't forget to brush your horse. You will CONSTANTLY see your horse's heart turn red. That is an image of the brush. Your horse is very needy. He needs to be constantly brushed. I make it a habit that whenever I get back on my horse, to brush him before I take off. This helps keep that heart core full as well as quickly improve your bond.
If it flies, it dies - killing things is the best way to earn money. Buy the varmint rifle early, and whenever you see a bird in the air, be sure to kill it. Birds are the best because they provide meat to cook, as well as flight feathers which are needed to craft improved arrows and all other manner of upgraded arrows. These arrows are mandatory for many of the challenges should you pursue them, but are also a great addition to your archery game. Birds' feathers can be sold, getting you around 50 cents each, just don't sell the "flight feathers". Killing rabbits and squirrels with the .22 will quickly give you some cash without taking up any space on your horse. Now carcasses will get you more cash at the trapper and butcher, but you have to return to them within a day or two in game or the carcass will rot and then you end up with nothing. A skin is better than nothing, but a carcass will get you more. When I know I'm about to make a trip to the trapper/butcher, then I will keep a carcass. You can store one medium carcass on your horse along with two small animals. I tend to hold onto rabbits since they are plentiful and you can store two of them. I tend to only chase perfect pelts though. You may have to kill an animal at two stars first though to learn its' anatomy, and then you can start getting 3 star perfect pelts provided the animal is healthy enough. Just be aware of that and don't kill yourself outright trying to find a perfect skin/pelt for a newly discovered animal. Try to learn the animals you encounter most and which will get you the perfect pelt. Racoons, badgers, squirrels, chipmunks, rabbits and all birds are 22. Coyotes and Foxes are your repeater. Big animals such as pig, boar, deer, elk, moose, cougar, ram and bison should be rifle. I like using a scoped rifle, but if you prefer to get in close, the Springfield or Bolt Action Rifle will do the job. I typically use the latter if the animal discovers me and I have to chase them down while on horseback.
Beware of cougars - if you dismount and are hunting, but sure you have one rifle that can kill a cougar that ISN'T scoped. A cougar will close distance fast and not even dead-eye can save you. Always have a bow, or Springfield or Bolt with you, or if nothing else the sawed off shotgun in your pistol holster. You will destroy the pelt, but at least you'll live. Save often too. Remember that if you have a legendary pelt or animal on your horse and you die, it is gone. I've reloaded many games just to not lose my legendary animal. Yes, you can re-hunt it, but why bother if you save often. Also be aware that any carcass or pelt that is tied to your horse (the large ones, not the multiple medium animal pelts that look like a blanket on your horse's rump) will fall off if you crash your horse. With all horses seemingly magnetized to crash into trees, this happens often, and in my frustration I just want to hurry up, keep back on my horse and ride away. Don't forget your valuables when you crash before your getaway.
Learn how to read a topography map - your minimap is a topography map. I have the benefit of military experience but many might not. So remember that a thick line on that map is showing you a cliff. Many are just thin lines. This shows you a gradual incline or decline in the elevation of the land. But if you see a thick line that looks bigger than the rest, this is showing you a cliff of some kind. Learn to read the map so you can properly navigate the county. This skill will only benefit you as the game progresses.
All premium cigarettes have a card - as you play, you will discover cigarette cards lying around. You can also collect cards from premium cigarettes. You will no doubt fill up your satchel though since in the beginning you can only hold 5, and even when you get the final satchel to hold 99, you will quickly fill that up. If you care about finding everything in this game, remember to always drop one premium cigarette when you are at max to pick up that next discovered premium cigarette for the card. Hold right to open up your satchel, hit R1/RB to navigate to the next screen, and then find your cigarettes and simply hold square/X to drop one. Or you could smoke one then and there if you need some deadeye. I often found 2 or 3 premium cigarettes together though and if you do them consecutively, you don't get the benefits, not to mention losing stamina core. Just be aware.
*********POSSIBLE SPOILER************ I don't think it is, BUT just to be sure -
Stay off the beaten path - this game has a TON to offer those that explore, but you will never find anything if you just stick to the roads. Map your destination, set your waypoint and put those newly acquired topography skills to the test. You will very often be rewarded with a stranger encounter, some oddity like a house or corpse or even loot.
Get your guns cleaned at the gunsmith - Gun oil costs over a dollar, but if you get your gun cleaned by the gunsmith in town, it will only run you a few cents. Save your gun oil for unique weapons that you use which the gunsmith will not clean, or when you are in the field for a long time and have no choice. Much cheaper to just let the smith clean it.
Fishing is hard - I only just discovered the secret. You DO NOT rotate the right thumbstick as quickly as possible. You just do a smooth, circular motion with the right thumbstick while pulling down on the left thumbstick, let go, pull down, over and over until the fish is in. You make the most progress pulling the fish in with that downward motion and when the fish gets close, you will see it. Fish close to yourself if you can, especially at first to see this, and you will be a pro in no time.
You can cycle what you want to pick up with the R1/RB - many times I found myself circling something I wanted to pick up instead of picking up a body or gun. If you watch the lower right corner, you will see bubbles appear when you are over more than 1 object that can be manipulated. Want those coffee grounds, but that stupid stranger's body is on top of it? Just hit R1. I spent the entire game circling to get in just the right spot to pick something up, or tossing bodies further away from collectibles to get everything. Don't be like me.
And that's my unique list. The first one is said in other places, but I felt it bared repeating because it is so valuable. Hope this helps if you are new to RDR2. Enjoy.