In your heart, you already know what is right for your project.
Trust in your instincts and know when something is just so. If you want to improve something, then ask yourself whether this is out of fear or necessity. Learn to be the judge of your own work and pay no heed to the criticism of others.
Some criticism can be useful, but a lot of it can be discouraging, especially if it comes from people who don’t understand what you’re trying to achieve. You are the person who can envision your project the clearest, so trust in your own criticism and judgement. Unfortunately, a lot of artists are overly critical and beat themselves up too much, but it is through evaluation that we create masterpieces. The trick is to find the right balance and go easier on yourself where credit is due.
Lately, I have surprised myself with my intuitive editing. I just seem to know when something is as it should be or when it needs to be tweaked. I suppose it helps that I tend to whip up pretty good first drafts, but even so… my editing skills have definitely improved! I am currently sorting out my third book and I can say with full confidence that you definitely learn more about the craft as you go along.
What I usually do is read through my manuscript and highlight any bits in red that need fixing later. Other things, like typos and grammatical errors, can be fixed straight away. I very rarely have to do much major restructuring because I plan my stories in advance, so my editing mainly involves tightening up the prose and removing redundant words.
Whatever project you may be working on, remember that it is your creation and you should know what’s best for it. There’s plenty of advice online if you’re unsure what to do or need to brush up on your technique, but you’ll learn a lot with experience. Just keep at it and keep sculpting your project until you sense that it is complete.