You can find lots of online mock tests for TISS exam at the sites mentioned below:

• https://mba.hitbullseye.com/TISS/TISS-Mock-Test-Question-Papers.php
• https://www.tcyonline.com/tests/tiss
• https://www.tcyonline.com/exam-preparation/844348/tiss-net

After giving mock tests make sure you analyse the solutions of each one of the thoroughly which will help you in overcoming your mistakes and come up with a strategy to definitely improve your marks and percentile. It will also help you to know about your strength and weakness which will help you in attempting easy questions first, that will reduce your chance of committing a silly mistake in an easy question or missing out an easy question. Along with this, you will also get enough time to attempt medium level difficult questions which will overall increase your speed with accuracy which leads to increase your percentile.

All the best!!