a really helpful thing to do is to force your mind to be in that moment and STAY in the moment. That was one of my biggest flaws while acting. It takes a while to exercise your brain to do that, but you just have to keep it focused and not let ANYTHING distract you while you're acting. Another thing you could do are some acting exercises (they basically help you focus). You can find them anywhere really. Hope this helped :)
Watch great movies and shows and really really pay attention to how they act then you might find that you did way better. Then practice with friends and family and show them what you can do. ;) GOOD LUCK!!!
I'd practice scenes from movies and film myself, I would then watch the original scene and the one that I did. I would then adjust loudness of my voice to match the scene fix my facial expressions and try again until I have the same emotion that the actor/actress is trying to portray. Show it to some friends and ask them what they think maybe! But have fun it doesn't have to be a sad scene! Hope this helped!
Become a stage actress all the best actors and actresses started on stage. And watch the old old films like "Gone with the wind" "The Wizard of Oz" "Casablanca" and others from around this time. Hope this helps and good luck.