Some possible improvements

Tasks you can undertake without affecting what other people are working on for the most part.
Implement colour tagging of cards.
Implement delete option.
Separate out a 30% area on the bottom of menu page, for putting a bunch of options/graphics
UI Improvement. (especially adjust font sizes.)
Make graphics for app.
Make random card mode not switch to the card it just showed.
Add syncing with firebase.
Work out bugs on android (needs android SDK) (Some corners are square instead of rounded for some reason).
Bug hunt

Also if you can, test the app on your phones. To make sure the performance is still ok. For me it is already lagging badly