WBJEE is easy to crack if you are focussed in your studies. If you have completed your syllabus, and also solved the previous year question papers, then it's pretty easy for you to crack WBJEE.
Now, for Jadavpur University, you have to rank below 500 for geting a chance in any branch, and below 300 (to be on the safe side) for getting CSE.
Hope this answer helps you.
Refer some reference books as mentioned below -
Concept of physics by HC VERMA
OP TONDON CHEMISTRY
Rd Sharma Mathematics
Arihant practice book for WBJEE.
For Jadavpur University you need rank under 300 as we all know that seats are very limited and admission is directly based on merit rank.
Feel free to comment if you have any doubt