Improv games can help!! I learned a couple at my Musical Theatre Camp.
This is a shoe (my favorite) stand in a circle with everyone. The first person says this to one of the persons next to them, (and the circle keeps going around in the same direction) 'This is a shoe' the next person replies 'a what?' 'a shoe' 'a what?' 'a shoe' 'ohhh a shoe' and 'takes' the shoe (The shoe is imaginary). You can do anything you want, speak another language, pretend the shoe is stinking, pretend the shoe was in a car accident......... Sob, cry, laugh, anything you want! But it's still a shoe. Amazingly fun!!
What are you doing? Everyone line up in two lines, facing each other. The front person steps out and pretends to do something (putting on makeup, jumping jacks, acting like a pterodactyl, ect) the front person from the other line comes up and asks 'what are you doing?' The first person responds with something different than what they are acting out. The second person starts doing whatever the first person told them they were doing. You keep going back and forth, trying to think up actions on the spot. Very fun!!
I can't remember the name of this game so let's call it STOP. Two lines like WAYD, this time both people step up and start talking about anything, or maybe they pretend to fight, anything they want. The the first persons in line go back and forth saying STOP, when someone says stop, both in the middle stop what they are doing, freeze in place, basically. The person who said stop takes one person's spot and they act with the other on the spot. Keeps going into eternity very fun!!
Okay, now on to working on skills. Talk about your characters. Find out everything about them. Find their motivations, fears, happiness, weaknesses, strengths, everything. Teach them to become their character, help them feel how their character is feeling.
Work on facial expressions, maybe rapid fire calling out different emotions for them to adapt to.
Work on diction, maybe your character has an accent. Maybe the character had a lisp. Learn to speak how your character does.
Now, these kinds of things scan take a while to learn. Be persistent. Don't give up. Just keep working at it, and someday you'll get there. You have a lot of time, that's a lot of days. And (unless this is a school project or needs to be made for a certain event) don't worry about the due date.
Most of all, have fun this should be a great group bonding activity. Don't let the director go power crazy. Make sure everyone is having a fun time, because if they aren't they might leave. And others will leave. So have fun!!!
I wish you the best of breaking limbs.