Common strategies for playing outside bets in online Roulette include focusing on bets like red/black, odd/even, and high/low due to their higher winning probabilities. The Martingale strategy involves doubling bets after each loss to recover losses, while the D'Alembert system gradually adjusts bets by increasing one unit after a loss and decreasing after a win. Flat betting, where players maintain the same stake throughout, helps manage the bankroll effectively.