The safest way to earn bitcoins is by earning bitcoins through signature campaign,on the other hand i would not suggest you to go for gambling as you will end up loosing as it is quite addictive and dont fall for it.On the other hand ,you can do trading,well if you want to take risk,you can earn a lot of bitcoins.
Trade is not a very risky way to make a profit, you just need patience and study information about strategies.