Kate
I sympathize with your having such a large class!!
Here are a couple of suggestions:

Continue to use flashcards as you are doing. Also include lots of visuals as well, i.e. pictures.

Have students do lots of hands-on learning group project activities- with these done in small group settings.

Use lots of role-play activities, as well as activities that require student participation.

Think of your role as being a "Facilitator" instead of a lecturer. This helps the students develop critical thinking and questioning skills.

Most importantly- make the learning fun for the students!!