Anything can be a project, and it's not really necessary to deliver a game-changing software at the end. Your project can be renovating your apartment for sale, learning a new language to relocate or increase the sales on e-commerce website for 120%, and these are just few examples.
For me personally project management is just a fancy and resume friendly word for getting things done in a specific time period, to ensure your progress.
So how to complete successfully a project? The question is more rhetorical than logical as success's definition is drastically different for people. For me personally success is progress, it can show that we're doing everything right or we should stop the project and move on. Progress and as many dead-ends as possible, to ensure you're going in the right direction.
If you're a project manager, then welcome to the club. I started at 2015, when I did not knew anything about the process of managing something like this, and as a 22 y.o. it was really exciting for me to finally get more responsibilities then I had. First two projects that I led were failed. My company defined a failure as not meeting deadlines and having a major scope creep, which I had. What when wrong?
Doing work by yourself
My biggest problem was doing everything my myself. At that time (sometimes now too) I was trying to solve every issue alone. There was no sense of team for me (while that did not bothered my teammates at all), I was doing everything faster and more structured and was taking all responsibilities, which led to a problem where my teammates decided to leave all the job on me.
Definition of project manager is to ensure that everyone is working on their scope and everyone on the team is involved. As project manager you should be focused on bringing on little pieces together and helping everyone to communicate well, not doing everything on your own.
Not listening to the team
Your team are the people you're going to work very closely for a very long time. Thus you need to create an environment of mutual respect and trust while managing the project. Trust is the major component in this and the thing I was struggling with the most. I tried to review and recheck everything while it took a very big time from me it also affected the deadlines and contributed to the team's internal environment. The only thing I needed to do is to accept that the team that I have is consisted of professionals, that know what to do.
Picking the project management methodology that works
Scrum, Kanban, Waterfall and many many other methodologies that come out every single day, claim that they are the newest and the best way to get the job done. While at first I was trying to keep up the tendencies and work only with the latest versions and methods, after a few projects I understood that there is no one method that rules them all. It is always about the people. If your team likes to share their experiences you can use scrum sprints and retrospectives, if your team likes to write tasks you can add kanban boards and at the end you may have mix of different methodologies that will work for your specific case. At the end of the day it is now about managing the people, it is about setting up a process that works.
During 5 years of project management I led 18 from which 6 failed. I love to share failures, they are guarantee of the progress. When I was talking about my failures no one shared theirs, but maybe everyone is perfect but me :)