When Implied Volatility is Low:

1) buy puts
2) bear vertical spreads: buy ATM call/sell ITM call or buy ATM put/sell OTM put
3) buy ITM call calendar spreads or buy OTM put calendar spreads


When Implied Volatility is Moderate:

Borrow shares and sell short the underlying


When Implied Volatility is High:

1) sell calls
2) bear vertical spreads: buy OTM call/sell ATM call or buy ITM put/sell ATM put
3) sell OTM call calendar spreads or sell ITM put calendar spreads