Hello, I have NMAT on 5th December, Snap on 10th,18th and 23rd December and Xat on 8th Jan. Can anyone suggest how I should go about preparing for these exams now that Cat is done. Should I prepare them one at a time or simultaneously?

In addition to the above suggestion. I feel that the areas you reckon you are weak in , should be worked upon. Mocks are not magic which will miraculously increase your percentiles just because it is a different test. Work on your weaknesses and try to bolster your scores in your strong areas.

Hi, if you prepared well for CAT, you just need to take Mocks for the exams and Analyse them seriously.
As NMAT is your next immediate exam, focus on NMAT - take mocks, review you mistakes and have a good strategy for the exam day.
Post NMAT, focus on SNAP and XAT. Try to dedicate enough time for XAT, as it has an entirely new section called the DM section. You need to prepare for this section well, along with taking good number of mocks.