Do not check your mobile phone at night.

Leave your mobile phone outside your bedroom at night. Instead, use a regular alarm clock to wake up in the morning, or a lamp that wakes you up with a gradually brighter light (a so-called wake-up light). 

WHY IT HELPS:
The bright light from your mobile phone is like a shot of espresso for your brain. The sudden exposure to blue light causes the release of cortisol, which inhibits the production of the sleep hormone melatonin. By leaving your mobile phone outside your bedroom, you also avoid the temptation to waste time on apps or social media.