Avoid waste of time as life is so very short indeed.
Just as I consider meditation quest, search, and explorations as the best utilization, and having the time of your life, quite a few things that we do are a waste of time really.
The following are a few examples though you may write a different list according to your own whim and understanding.
Socializing all the time and doing hardly anything else
Spending much more than necessary time on phone, Whatsapp, Facebook, Twitter, Internet etc.
Watching excessive cable TV, or movies
Eating a lot of junk food
Playing cards, video games beyond a certain limit
Talking and talking unnecessarily, or gossiping endlessly about somebody or the other