The safest way to gamble is to start gambling without depositing. At least, if you lose, you just lost time.
What I like to do is to use XAPO Faucets, once I reached the minimum amount I can send to another bitcoin adress (5500 satoshis) I put them on a multiple events sports bet I make on DirectBet.
Even if the odd is around 2. I make a "safest" bets possible so I can reach higher amounts pretty fast.
Just imagine you bet on a 2x payout sports bet, everyday starting with 0.000055.
In a week (7 days) you get: 0.000055*2^7=0.00704 bitcoins. Then 5 days after 0.00704*2^5=0.22528.

If you lose, no problem, just do it again, until you reach a great amount. And learn to stop. Do not get greedy.