can i crack iit jee in 6 months.I didn't complete my 70% of my concepts.please give any tips.

Yes, you can  crack IIT JEE exam in 6 months but you need to clear your concepts and you should build your base strong.

You can follow below recommended books for your preparation

Physics: NCERT Physics, HC Verma (That’s  the best book available for physics),Arihant by DC Pandey
Chemistry: NCERT (Dont miss this one)
Physical – P Bahadur
Organic -Arihant
I norganic – P.Bahadur/OP Tandon
Mathematics:
ML Khanna or RD Sharma

You should refer previous year papers to understand the exam pattern and level of questions. You should focus on important topis and try to solve as many as mock test series to analyze your preparation level.

Noo books better than ncert if u r aiming for any nit than surely ncert books will help u

You can refer to some books published by "CENAGE". They provide you excellent preparation . There are wide range of books for JEE mains & Advanced , which are published by "CENAGE". Referring those books builds a strong foundation on concepts.
I hereby think this may help you .
Yours faithfully,
ngu ^-^

Of course you can. Believe on yourself. First clear all basics in physics and then must do h c verma. For chemistry ncert is enough. Learn chemistry word by word from heart. For maths do Alzebra book of arihant and do rd sharma too. In February do last year question paper and do your best...