That's a great question.  I can relate.  I have a tendency to occasionally make small mistakes (such as changing `-` on one line to `+` on the next).  

I first look at what my mistakes were. 

• If I am not sure why an answer was incorrect or why my method did not work, that probably means I need to increase my understanding of the subject.
• If I can see my mistake and understand how to do it correctly, then I think about what I can do to minimize making the same mistake again.  Can I do a bunch of similar practice exercises until I automatically do it correctly?  Can I get in the habit of checking my answer by plugging it back in to the original question?  Would it help for me to proofread my steps?  Should I do more of the work on paper rather than in my head?

Once I do that, if I am getting 95-99% correct answers, that is probably good enough.
If it is still under 95%, I might ask someone else to help me brainstorm ways I could make fewer mistakes.

Does any of that help?

P.S. You can find me on the main part of the website answering 6th grade math questions.