Best way is to meditate in the morning after you’ve had a good night’s sleep. If you find yourself sleeping even in the morning, go to bed earlier. If for some reason no time of the day works for you, consider that sleep deprivation is a bigger problem than whatever you’re getting into meditation for.
Another thing to try to do is to use an object. The breath is a good thing to focus on, make sure it’s slow and regular. Read a book on concentration meditation and try to progress through the jhanas.