There are several no-no's when trading covered calls. You can go back and read how I've made some of these mistakes. They are actually easy to avoid, if you just take the time to learn.
No-no #1) Not doing your homework. The only way to make money in the market (I should add consistently) is doing your homework, and doing it better than 80% of the rest of the schlubs out there. And this is key. Forgetting say, fundamental analysis, might lead to something catastrophic. If you ever go long and buy a stock, you want it to be a profitable company--not a looser sitting in their mother's basement.
No-no #2) Failing to manage the trade. Covered calls are a simple to manage--not like herding a flock of pre-schoolers down El Camino Real. But, you do need to watch it. A covered call will give you some down side protection, but does not eliminate risk. Stocks can still go to zero! Make sure you have a mental stop set up for the trade. The short call can give you downside protection of up to 11% or thereabouts, but it is no long Put.
No-no #3) Trading the wrong strategy. Don't do what I did, and trade covered calls on LEH right before they announce their first losses ever. Catastrophic. If I wasn't sure which direction that was going, but knew that whichever way it was going was going to be the bootleggers car of them all.... I would have Straddled or Strangled long. (As a beginning options trader that was not available to me, and instead of staying out, I did the No-no). A stradle would have captured this and made me a lot of money, but I digress.
No-no #4) Writing calls with too much time. As a buyer you want time on your side, so buy way out, buy LEAPs if you want. But as a seller, too much time can hurt you. Don't sell a call 6 months out, the premium may seem bigger, but in actuality you are going to make more money selling calls 1 to 2 months out from expiration than any other. Watch time drop like a led balloon.
Trade right and returns will come.