Here are some things to consider if you want to employ a covered call strategy for consistent returns. The discussion also applies to written puts, as they're functionally equivalent.
Write covered calls only on fairly valued stock.
If the stock is distinctly undervalued, just buy it. By writing the call, you cap the gains that it will achieve as the stock price gravitates to intrinsic value.
If the stock is overvalued, sell it, or just stay away. As the owner of a covered call position, you have full exposure to the downside of the stock. The premium received is normally way too small to protect against much of a drop in price.
The ideal candidate doesn't change in price much over the life of the position. Yes, this is low volatility, which brings low option premiums. As a seller you want high premiums. But this can't be judged in a vacuum. No matter how high the volatility in absolute terms, as a seller you're betting the market has overpriced volatility. If volatility is high, so premiums are fat, but the market is correct, then the very real risk of the stock dropping over the life of the position offsets the premium received.
One thing to look at is current implied volatility for the at-the-money (ATM), near-month call. Compare it to the two-year historical volatility (Morningstar has this conveniently displayed).
Moving away from pure volatility, consider writing calls about three months out, just slightly out of the money. The premium is all time value, and the time value decay accelerates in the final few months. (In theory, a series of one-month options would be higher time value, but there are frictional costs, and no guarantee that today's "good deal" will be repeatable twelve time per year.)
When comparing various strikes and expirations, compare time value per day.
To compare the same statistic across multiple companies, use time value per day as a percent of capital at risk. CaR is the price of the stock less the premium received. If you already own the stock, track it as if you just bought it for this strategy, so use the price on the day you wrote the call.
Along with time value per day, compare the simple annualized percent return, again, on capital at risk, measuring the return if a) the stock is called away, and b) the stock remains unchanged. I usually concentrate more on the second scenario, as we get the capital gain on the stock regardless, without the option strategy.
Ideally, you can also calculate the probability (based on implied volatility) of the stock achieving these price points by expiration. Measuring returns at many possible stock prices, you can develop an overall expected return.
I won't go into further detail, as it seems outside the scope here. Finally, I usually target a minimum of 25% annualized if the stock remains unchanged. You can, of course, adjust this up or down depending on your risk tolerance. I consider this to be conservative.