I wait for a run of 6 (or more) red or black. I walk up, place a bet (say $20) on the opposite color. Most of the time, I win right away. If I lose, I will double down (double my prior bet on the same color, so $40, $80, $160), but no more than three more times. Outside the first time I did this (and chased a $20 with over $600, realized what I did and set my rule!) I've never had to go past three (so 4 bets total)
And that's it. Statically speaking I always have the same slightly less than 50/50 chance of winning (thanks to 0/00 it's not even odds although it pays that way), the prior spins really don't make any difference. Except, when I play this way, I win.Like I said, statistically it shouldn't work. Call it luck I guess.
The downside is you need a busy casino (with busy tables, which is getting harder and harder to find even in Vegas these days) that allows cash or casino chips on outside bets (bets along the outside of the table for color, odd/even, etc) at their roulette tables vs making you buy table chips, which for roulette are specific to the table. You will not get rich playing this way, it's too slow and higher bets risk running into table limits if you start doubling down, but it's an easy way to pay for dinner.