Nervousness will only bring stress which can lead to silly mistakes in the exam. So don't be nervous. 

For Physics :- Read and understand the concepts. Revise everything that you have studied. Revise formulas. Practice numericals. Mark the numericals which are tricky and revise them. If any doubt arises in concepts then get it cleared as soon as possible. 

Don't get stressed. Be confident and give the paper. 

JEE Mains is again going to take place in April so if you have any preparation queries regarding that do mention it down in the comment section.