Martingale is a betting where you only lose if the opposite color that your betting on goes on a losing streak. You do a very small bet on a one color and if you lose the bet you double the bet. So say you bet 10 coins and lose, you double it and go to 20, if you win you go back to the original bet of 10. As long as you bet smart, and aren't very unlucky, you will profit a lot... but this startegy is very time consuming.
You Bet 10 Coins and Lose
You Bet 20 Coins and Lose (Total Bet 30 and Profit 10)
You Bet 40 Coins and Win (Total Bet 70 and Profit 10)
A lot of websites require a deposit to be able to withdraw. High-risk/reward betting can make you a lot of money. Rather than doing spending 20 minutes per site, just going all-in on green can profit big-time and save lots of time. Going site-to-site using referral codes until it lands on green is a great idea on how to get skins fast!
Rather than going for high cashout numbers, auto-betting with low cashout numbers can be a safer bet to make. Having the auto-bet set to cashing out at 1.05x to 1.15x only fails if it instant crashes. Of course you could go for a 4x multiplier, but it is very lucky/inconsistent.
All or Nothing
This method is more common sense than anything. Betting a very small portion of your balance and going for multipliers such as 4x and higher. This way, you can make a lot of money very quickly, but you also stand the risk of waiting a long-time for that multiplier and draining your balance.