CAT

CAT is concept based exam where you need higher accuracy. You have plenty of time during examination. Once you are clear with your concepts, you can easily score 90-95 Percentile.

Keep your self updated. Read newspapers, u need to have good vocabulary, books are available in the market for the preparation for CAT.
For more help, you can join any of the coaching classes which offers CAT preparations.

It is very hard to say, but you can refer the following link to get a fair idea
http://www.iimrohtak.ac.in/admission/wat-pi-2015.html.

The CAT cut-off at Ahmadabad is always around 99.5 pr.

Just be aware of what you wrote on your CV and follow the current affairs. 90% of the present batch is above 83 percentile. So, you have to do pretty well in the GDPI to make the cut

CAT score will make you eligible for all India quota seats in Maharashtra which generally have higher cut-offs. The colleges such as JBIMS, SIMSREE, SIMSR, Welingkar, SIES, PUMBA have 99+ Percentile cut off for CAT. You can appear for CET now as forms are out and score higher than CAT score for getting better college.

Your CAT score is low, but BITS Pilani's MBA follows a profile based selection and it is not just the CAT percentile what is looked upon for admission. So, I would suggest you to apply for it.

It depends upon you that what matters to you. BITS Pilani MBA is a good choice this year, but if you feel that you can score better in the next year, I would suggest you to go for it.

Nirma University for MBA is quite average university, because it doesn't have a very good alumni background, and the safe score in CAT for getting into it is 500.