I will most generally choose a hot ball as a key number. I do search drawing for the history of a ball.
The 18 ball dropped last night 08-11-18-22-27
I played 3 lines and had the 11-18 on two lines.
Maybe I will start looking into a key pair possibility. That will give me two balls for a line and will only need to select three more balls to go with the key pair.