Here are some preparation tips given below you can follow for NIMCET exam preparation.

Go through the previous year papers, It will help you to know the level of the questions and do practise as much you can.

Make Schedule for preparing - You should divide the time as per the subjects of the exam as this exam contains 5 sections including Analytical ability & logical reasoning, Mathematics, Computer awareness, General English and Quantitative ability,also keep some time for revision. Make short notes while learning that can help you while revision.
Improve verbal and non verbal reasoning and analytical -There are several books available in the market that one can refer to improve his reasoning skills. Also, to clear the concepts it is good if you have a guide who can teach you to think out of the box while going for reasoning questions.
Improve English language skills - It is quite common that candidates score low in this section as English is not he first choice of language for many as one must work on his grammatical skills and there are many books available in the market for this purpose.

You can check the App on the internet but you can rely on that for the exam preparation.

You can check the exam syllabus with the given below link.

Https://it.careers360.com/articles/nimcet-syllabus

Good Luck!