if anyone can get 789 rank in wbjee, then what should he/she do??

Dear Aspirant,

At first many many congratulations for your outstanding success in WBJEE 2020.
As we all know that West Bengal Joint Entrance Examinations Board (WBJEEB) hasn't released the official cut-off details for the topmost and eminent Engineering instituions in West Bengal, so I would like to suggest you to follow the cut-off trend of previous few years regarding your query. Though the cut-off details change every year based on several determining factors like number of appeared canditates, number of successful candidates, total number of available seats, toughness level of examination, but you can definitely get a primary idea about the qualifying details of your desirable instituions.
Ok, now directly come to your question. Considering you as a General-UR candidate (as you haven't given any information regarding your category in your question) I want to inform you that with your rank you can easily get admitted in the best Engineering college of West Bengal i.e. Jadavpur University  in almost all departments excluding Computer Science and Engineering , information Technology and Electronics and Telecommunications.

But one thing should be added here is that if your dream is to be an eminent computer engineer or software engineer in future then you should go for CSE or IT in other topmost and esteemed colleges. And it's a matter of great pleasure that apart from JU, your marks and rank are perfectly suitable for CSE department in any other Engineering College in West Bengal. Hence I should recommend you to go for IEM (Institute of Engineering and Management) ahead of any other Government colleges due to greater placement records (i.e. despite being private Engineering college, their placement possibilities and packages are undoubtedly better than any other Government colleges in WB).

On account of being private Engineering college, the fees structure of IEM must be high (i.e. almost 90k per year). If you've any financial issue regarding this but still you want to be an Computer Engineer so I suggest you to take admission University of Kalyani in that case, it's also undoubtedly a renowned Government college in WB.

Now I want to refer you the previous year's (2019) cut-off details of WBJEE for all top institutions through the link given below to ensure your admission chances:

https://university.careers360.com/articles/jadavpur-university-cutoff

Also you can go through the Carrers360 article provided in the following link to gain a clear and detailed perception about the topmost and eminent colleges in WB :

https://engineering.careers360.com/colleges/ranking/top-government-engineering-colleges-in-west-bengal

Predict your colleges from the Careers360 JEE MAIN college predictor tool:

https://engineering.careers360.com/jee-main-college-predictor?icn=QnA&ici=qna_answer

Besides, if your rank is so good in WBJEE then your rank must be also impressive in JEE MAIN. So you must opt for JOSAA counselling as well as try in JEE ADVANCED.

Hope these informations and links are quite significant and more than sufficient to diminish your query.

All the best!!