Most of the time preparation for this certification exam is approached in the conventional style especially the way you did preparation back in school and college days. However the reality of this exam is that you are no longer in school or in college (some exceptions maybe there) you are in a full time job and you have to manage job responsibilities and also are going to study after a break. Hence the preparation approach must be also different.
Rather than beating yourself up for not studying the way you did earlier design a new approach as the circumstances are different now. Make a study plan keeping the reality of the current circumstance in mind.
The SCJP exam now-a-days having more coding questions. Small code snippets are given and either with compilation errors or code logic errors need to be answered.
Practice practice practice...
SCJP questions can be best answered if you have done hands on programming in Java and if not then you will need to practise many such questions that give you exposure of coding. Look for mock tests/sample practise tests that have you practise a lot of coding.
Preparing for the certification exam alone is a trap you will never be able to study alone as you have never done that in school/college etc you had your entire class friends preparing with you.
get a group of committed people to take the exam with you
Get a friend/colleague or register in a Java forum to belong to a group of people and prepare along with them. Not only will it be fun but it" also give you the required competition and keep you on your toes.
You might have heard of this great person in your office who passed the exam in 1 week or 1 month and now you are impatient as to how long it will take for you to be certified. You plan for 1 month and soon the plan goes to the dogs so now you are really impatient and in your mind you have made it a very tough exam that will take lots to pass.
Build brick by Brick
Don't try to learn the entire language in a week/month, take your time. Keep the objective of learning and not just somehow passing the certification exam. Learn "why" something works a given way, not just that it works one way. This will surely see you long way in your journey as a Java professional.
This is a tough one to answer. And exam will always be an exam meaning it will always give butterfly in your stomach and make you feel like throwing up the moment you think of taking the exam.
Don"t be guided by you feelings
Here again I will point to the first point, keep in touch with the reality of your exam preparation. Let the scores in the practise tests/mock tests guide you whether you are ready for the exam or not. If you are scoring 85% + in the mock tests do go take the exam.