As the other commenter said, examples of where you struggle would really help people provide feedback here. Show us a problem, your line of reasoning and proposed answer, and then the answer that you were told it actually was.
In general, factorizing can be quite difficult. There are basic things to check that you should get accustomed to. There are go-to theorems that give you a framework to work with when it's really tricky. But a lot of the time the key is having enough practice and experience with it that you spot neat tricks and shortcuts. That kind of thing is difficult to just hand someone without having them put the work in.