I've used covered calls in the past with good success. They are safest when used on stock that is not so volatile such as consumer durables, such as Colgate, Procter and Gamble, Pepsi, Clorox, etc. You won't get the premiums that you can get with a more volatile stock. However, if you sell call options on the more volatile stocks, you lose flexibility to get out if the stock takes a large dive. You must buy back the option and take a loss on the option as well as the stock.
From both good and bad experience, I prefer to sell options on stock that is not likely to move up or down a large amount and to set stop losses on volatile stock.
By the way, sometimes when an option is exercised, you make a better return than you would have made if the option had expired below the strike price. I use a spreadsheet to calculate the two scenarios.
Stephen