How to save from tax exemptions?

Hi, I am new to the IT world and I have been earning more than 5 lakhs. so each month some tax deductions are being done on my salary.

I pay rent of 5700 and am also going to open a LIC policy for the same.

One of my seniors said that, instead of 5700, you declare 8333 in HRA and show some declarations at the end, and you'll be good.

I just want to ask, isn't it illegal to show fake declarations? or is it practiced like that only? kindly help me. I have very little knowledge about this