Selling a call spread is a bearish play. Selling a put spread is bullish.

Look for IV above 50% to collect more premium. Volatility at extremes tends to revert to the mean (the middle or 50%) over time. So selling above 50% gives you more premium and then it tends to get cheaper to buy back as it moves back to 50%. Of course IV could expand....it is just more likely to revert to the mean than to expand.