What are the precautions in doing newtons ring experiment?

So if you want Newton's rings to form all you have to do is make sure monochromatic light incidents on glass placed at a 45 degree angle and from there it should go to the plano-convex lens. What happens here is that the ray undergoes division of amplitude. So now two coherent rays emerge out of the plano convex lens. Since these two are coherent rays they interfere each other and form constructive and destructive interference. All the loci comes together and form bright and dark rings