Screen flickering in Ubuntu 16.04.lts

Recently I am having a problem of flickering screen on my Lenovo laptop where I have installed ubuntu 16.04 . It had also happened a couple of months ago, but was fixed automatically the next day after I connected my laptop to external monitor through HDMI where just mouse was flickering and same thing happened to my laptop screen the next day for a while and was fixed automatically. But the problem is now happening consistantly and is not solved. What can I do for that ?