Know When To Switch
Countering the enemy is a huge part of Overwatch 2. I understand you may want to play certain heroes or do things your way but winning the game will probably be more satisfying in the end. Picking to counter has a lot more benefits and after all it is a team game, and you will need to pick whatever benefits your team best. Don't be discouraged because you can always play your favourite hero next game! Also I recommend trying to learn a range of heroes so you avoid getting stuck if you need to swap and are unable to play a hero to a decent level.
Positioning
This one can be a little hard as each map has different points, low and high grounds and flanking pathways that you need to take into consideration. To practice I suggest going into a custom game and walking around in high speed looking at healthpacks and sightlines. Unfortunately a lot of the knowledge comes from actually playing the game since you will experience different team compositions and how different players think which can show you what to do or not to do the next time you play in a specific place.
Try Learn All Hero Basics
When I first started Overwatch I had never played a game like it and the mix of an FPS with such a unique hero selection made learning each hero and their abilities incredibly difficult. It is another thing that comes with time but luckily its not too hard to search up a guide (like mine!) to assist in your learning. Again, if you want you can go into a custom game, the practice range or even quickplay and tryout each of the kits on the bots before you play competitive.
Practice Mechanical Skill
For some this comes naturally but for most it does not. It either comes with practice from playing the game or from playing other FPS games. Try play aim trainers like KovaaK's for example which can help improve your raw aiming ability and muscle memory. If you put in the work you will see a difference but aim trainers are not the be all and end all so try not to rely excuslively on them.
Be Patient!
Progress is not linear; you definitely won't improve instantly and it will largely depend on how much you really want to improve. Putting effort into all the tips I suggested above will get you somewhere but you can go further by taking initiative and going into depth with your skills.