...is almost impossible. If you shoot for absolute perfection, you will always fall short. But that doesn't mean you shouldn't attempt it. Rather, you should not beat yourself up when you don't deliver a "perfect" reading.
Dropped lines, missed cues, and stumbling on dialogue happens. Just watch any "blooper reel" from your favorite TV shows and movies. That's why we have this thing in film and TV called "takes". Now in live performance on stage, you have to take that flub and "go with it", letting go of your error and keeping in the moment. But in film and TV, there's always a re-take.
Sometimes, a mistake can be thought of as a gift -- and actually enhances an audience's enjoyment. As an actor, you have to learn to "roll with the punches" -- never break until the director yells "cut"! Although there's evidence that certain actors may be able to control which takes are used by deliberately blowing takes that they don't like. But the only way you can get away with that strategy is by being a highly paid movie star who's name guarantees a #1 opening weekend and international distribution. Most actors would be wise to avoid this behavior.
In the martial arts, sparring is the ultimate "Improv Exercise". Here, all fixed patterns disappear and one is left with having to "be in the moment", responding to an opponent's attack without thinking too hard. In fact, the more you think about what to do, the more likely you are going to eat a head shot, and I'm not talking about an 8x10 photograph!
I like to look at auditioning like sparring. Though the dialogue on the sides will dictate what comes out of my mouth, the intention and emotion will depend upon not only what's happening in the story, but also the energy of the room. I don't mean going flat when reading with an assistant who doesn't put anything into their reading, but instead, being open to any emotional content that might manifest itself. If you've done your homework, you can let it all go during the audition, letting things happen organically. It's a bit scary, like sparring full contact, but that's where the magic happens.
If it sounds a bit Zen, that's no coincidence. Being "in the moment" is like having "no mind". The next time you have an audition, treat it like moving meditation. The results may surprise you!
Happy Acting!
