One of my favourite systems is the favourite number system which I have won with most of the time I have used it.
Many systems use progressive staking, but this one uses progrssive odds, so you are betting 1 unit each time. You target a single number and all your bets focus on that number hitting, but there are many chances of other numbers giving you a winner. If any of your bets win you will have a profit between 1 unit and 18 units, depending where in the sequence it lands. You need 35 units for this method.
1 attempt at an evens chance that includes your number.
1 attempt at a dozen or column that includes your number.
3 attempts at a double street that includes your number.
3 attempts at a corner that includes your number.
3 attempts at a street that includes your number.
6 attempts at a split that includes your number.
18 attempts at the single number.
When you win the session is over and you can start again preferably with a different number. A very simple system with no complex rules to remember.