Whether for stage or screen you must learn your lines. There is no excuse.
As veteran British actor Bill Nighy says: “You must know your lines inside out and back to front.”
If you don’t know your lines then you are not connected to either the moment or to the other actor(s).
There are numerous techniques available when it comes to learning lines.
If you’re a crammer, reading the lines over and over until they stick, then try highlighting your lines and stage directions with a yellow highlighter. This simple technique helps to decrease the amount of time spent cramming and memorising the lines as the colour yellow really stands out to the human brain.
Another technique is to download a rehearsal app to your iPhone and use the app to rehearse and remember lines. The same can be done with a small tape recorder.
Some actors cover the lines with a piece of paper and slowly move down the page memorising the lines as they go. This can also speed up the learning process by learning the text in short blocks as opposed to trying to cram it all in at once.
Yet another useful technique is to write or type the scene out numerous times. After writing the scene down say 8 times you feel like you’ve actually written it yourself and the the lines should stick in your memory.
Once you know your lines and you’re on set then start rehearsing with the other actor(s) and forget the lines – just listen to the other actor(s) and engage with them. If you are thinking about the lines then you are NOT engaged, you are stuck in your own head.
Remember, there is absolutely no excuse for not knowing your lines, therefore you must find a technique or a combination of techniques to achieve your goal.