Silly mistakes usually come from rushing, not reading the question properly, and weak exam-time habits, not from lack of knowledge, so you fix them by slowing down slightly, reading carefully, and building a checking routine. These are some of the most painful marks to lose because you actually knew the answer.
Read the question twice. A huge share of silly mistakes are simply misreading what is asked, missing a not, a unit, or a key word. A few extra seconds reading carefully saves marks.
Slow down just enough. Rushing causes calculation slips and skipped steps. You do not need to crawl, just write at a controlled pace and do not panic-rush, especially at the start.
Show your steps. In maths and science, writing each step clearly, not doing it all in your head, makes errors easier to catch and often earns method marks even if the final answer slips.
Keep an error log while practising. Note every silly mistake you make in practice and its cause, wrong sign, missed unit, misread question. Reviewing this trains your brain to watch for your specific traps.
Example: A Class 12 student in Surat kept losing 8 to 10 marks to careless errors. He started underlining keywords in each question and keeping a common-mistakes list. In the boards, those errors nearly disappeared.
One practical tip: For numerical subjects, quickly sanity-check each answer, does the value make sense, are the units right? This 10-second habit per question catches a surprising number of silly errors before you move on.