Play it safe means to always choose the option with less or no risks.
Example: He was afraid of losing money, so when he was in Las Vegas, he played it safe and only bet ten dollars at the casino.
Seize the day means to make the most of the present moment and opportunity. This may include taking a risk or doing something unusual because one has the opportunity.
Example: It was rainy during my trip to Berlin, but while I was there, I seized the day anyway and saw as much of the city as I could.
Watch the video below (and try not to laugh!). Which of these two types of person are you?