There are few entrances for MCA and the preparation may vary on the entrance you are planning to apprear for. Some of the general tips for your MCA preparation are:

• Know the enttire exam pattern, marking scheme, latest trends etc.
• Delegate time to each section smartly.
• Practice the questions which test your analytical skills. It will sharpen your concepts and basics.
• Practice mental mathematics questions. Without practice you won't be able to attempt it.
• In case you find it difficult, you can join any professional institute for preparation but its not difficult, by your own time and effort you can study by self.
• Go through previous year papers of the entrance.
• The important thing is to give mocks. Appear sectional/full length mocks. Analyse your mocks and results. Know your weak and strong areas and improve those sections.

These tips will surely help you to achieve your target.

Good Luck.