Can we crack bitsat 300+ in one year...iam taking long term and strong with my basics......and in mains what mark should i needed becoz my board score is less that is 88% andra pradesh to get into nit....

yes ...you can crack bitsat 300+..
The best way to crack entrance exam is by revising the subjects and the topics completed along with the preparing. It is very essential to revise as you keep on learning new things, chances of forgetting the things learnt increases. It is always advised to keep revising everyday for an hour or two, the topics that you have covered.

Try hard for JEE and BITSAT coaching.
One year is efficient for the practice..For Physics...G C Aggarwall and previous year IIT JEE papers.
Chemistry---- O P Tandon
Mathematics-- Cengage Publication..

Test series at last of the session