Selling naked puts is a good strategy, but you need to be aware of the risks. Only sell the number of contracts based on number of shares you are willing to own. If you do it, even if the stock tanks, you still will do better than owning the stock.
As for calculating gains - yes, you are right. I had a discussion with someone who claimed to have 100%+ gains around 90% of the time. Turned out his "secret" strategy that makes "100%+ gains around 90% of the time" was selling naked puts.
According to him, "100% gains is keeping the entire option premium that I received as the result of the option contract expiring worthless."
However, there is a "small" problem: when you sell a naked put, there is margin requirement. And the only way to calculate gains is return on margin. Depending on the stock and the expiration, your return on margin is usually around 10-15% if your sell slightly OTM puts. Nowhere close to 100%+ gain. Yes, you can win 90% of the time if you sell far OTM puts with deltas of 10-15, but in this case your maximum gain is usually 3-5%.
Unfortunately, internet is full of hype from people that will tell you what you want to hear. And this is what gives options a bad name.
Edited February 27 by Kim