Learning lines is probably the most common problem amongst new actors.
I know, Ive been there myself.
Using a voice recorder, writing them out time and time again, highlighting my lines, asking a friend or random person on the bus to test me, thinking I had them, then going blank, anxiety dreams about being on stage in front of hundreds of people or on set in front of high profile actors... and my brain fails me.
There's nothing there, my lines have gone!
"But what can we do about it?" "Stop learning lines."
"Have you gone mad?"
"Probably, yes, but that's besides the point. Anyway, allow me to explain..."
If you're learning lines, all you are doing is... well, learning lines - what the words are and what order they go in.
While you're learning you'll probably start thinking about HOW to say the lines as well. But it's meaningless.
Stop learning lines, and learn your role instead. Don't place too much importance on the dialogue.
The strength in the scene comes from what is going on BEHIND THE LINES.
I am not in any way suggesting that you turn up for your scene not knowing your lines, or that it doesn't matter what you say as long as you get the point across, because that would be wrong.
What I'm suggesting is that you allow them to sink in, rather than spend your time going over and over them parrot fashion.
Learn everything you can about your role.
Who is your character? What sort of background have they had? What makes them tick? How would they react in various circumstances? Why?
What has led them to this point?
The questions you can ask yourself are never ending. Become a detective and go through your script carefully, picking up any clues you can find about your role.
After you've done this, you make the rest up.
Make strong decisions and go into as much detail as you can.
Use your creativity and create a person, for you to step into their shoes and bring to life.
When you feel you know your role pretty well, get your highlighter out, but leave your lines, and highlight your reaction points instead. The points that make you want to say something or take action.
Bob: My house was broken into today, while I was at the football match.
Here I would highlight 'My house was broken into'
Bob: While I was at the football today, my house was broken into.
I would still highlight 'my house was broken into', but my response would be slower as I've had less time to process what has made me want to react.
Then, under each of your lines, write the thought behind them.
Mary: Hello Frank, it's lovely to see you.
Could be 'Wow Frank, I have missed you' or it could be 'Oh Frank, the last person I wanted to see'.
What we say and what we mean, often vary greatly and so I believe this to be a very important step.
After that, cover your lines, read the other character's line, then guess what your response would be, before uncovering your line to check how accurate you were.
By now, you will know your character well and your guess work will probably be very close.
If not, don't worry, just do some more character preparation and try again.
Once you are responding in the way you should, then all you'll need to do is tweak the words so that you are staying in line with the script.
Give it a go. You will probably find that, not only are you are no longer anxious about forgetting your lines and start to trust yourself more, but the scene will feel more natural as you are listening and responding rather than waiting for your cue.