Read the documentation carefully, pay attention, sleep well, take pauses and don't drink. Those may help in preventing making mistakes, but does not guarantee they won't happen. I'm a bit far from 22 years of experience in programming and still make silly mistakes. Good practices like the ones pointed by GrandFather will help spotting errors faster.
In your comments I don't see you helping missingthepoint either not making mistakes nor figuring them out.
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