Major Traps/Pitfalls in UPSC preparation

Scenario 1: Your GS syllabus is not complete and you decide to give a prelims attempt anyway. What are the repercussions??

Scenario 2-You have not practiced answer writing for GS or Optional but your syllabus is complete. How this becomes a vicious cycle?

and multiple such scenarios and way out of the trap-What is the ideal way to prepare. How much time you should give before you appear for prelims. Let's discuss.