How to choose what expiration and strike price to trade can seem daunting when you first look at an option chain. However, 90% of trades will probably do well to just stick with one general rule of thumb:
Expiration Date 30-50 days remaining, Strike Price at-the-money
That's it. Follow that rule for at least 90% of your trades.
Here's a little more information for the remaining 10% of trades.
As expiration approaches, time decay increases sharply. At 20 days remaining that time decay (theta) really kicks in. Keep your option trades in the 30-50 day sweet spot.
In-the-Money = Less % Risk & Less % Reward
At-the-Money = Normal Risk & Normal Reward
Out-of-the-Money = Higher % Risk & Higher % Reward
For example. If AAPL is trading at $200 and you want to buy calls, then a good place to start is with finding the monthly options expiration with between 30 and 50 days remaining. Then you would buy the $200 calls.
If you bought the same dollar amount of the $230 calls you would have higher potential percentage reward, but also higher percentage risk. If you bought the $180 in-the-money calls you would have a lower percentage risk, but also a lower percentage reward.