The best way to get better in parkour is to just play it a lot, this will get you comfortable with your controls and timing which will help you do harder jumps. Another thing is to learn how the physics works, as it makes it easier to understand what happens. You should try to learn some basic easy strats and timings that will be very useful. Make sure to get your knowledge from good sources. DO NOT LISTEN TO DREAM'S VIDEO ON THE LONGEST JUMP IN MINECRAFT. I cannot stress this enough. Learn from experts who actually do professional parkour and know what they're talking about. Getting misled is the worst way to embark on your parkour journey, sorry to be a bit ranty, but misinformation is the single biggest threat out there to our community. Too many times have big youtubers who have no idea what they're talking about tried to talk about parkour mechanics, and 90% of the time they just spread false information.
Parkour is very much a mental test. Due to it being partially luck based, it can get very hard, and you'll find yourself stuck on levels foe long periods, even hours, possibly. It is important to keep a good mindset and not to burn yourself out. Don't attempt anything that's too hard for you, a challenge is good, but don't overpush yourself. When you first join the world of parkour, the pros may seem daunting, doing insane jumps that you have no clue how they work. Do not worry. You will eventually pick it up. The best way to learn is to ask a pro about it. Since the community is small, info is limited, so word of mouth is the best way to learn. I recommend joining parkour discord servers, that's the best way to get comfortable.
Good luck!