Here's something that you can try that has proven very successful for me. I call it an Activity "Blitz".
Start by selecting four to six related activities. By "related", I mean that each activity has something in common – maybe have a "Puzzle Blitz" with different types of jigsaw puzzles for people with dementia, a "Game Blitz" with different games, or a "Traditional Montessori Blitz" with different traditional Montessori activities for dementia. It makes it easier to switch activities between residents and to supervise the activities if they are all related.
Set up one activity on each table (or at each end of a table if the table is long) in a common area. The idea is that each activity is separate so that distractions between them are minimized.
After the activities are set up and ready to go, invite one de mentia resident to join you. If the memory care resident is familiar with the activities, ask them which one they would like to do. If they are not familiar, make your best guess at a suitable activity and sit them at the appropriate table. Help them get started with the activity as you normally would. Once they are working away at the activity, invite the next participant and get them started in the same way. Have a volunteer (or second staff member) in the room keeping an eye on things and helping the residents as necessary. Continue to invite residents until everyone is in the room and engaged in an activity.
Move around the room and engage residents in conversation, help them if necessary and just generally have fun. As a resident finishes an activity, ask them if they would like to do it again or alternatively ask them if they would like to do a different activity ("Would you like to help me put the puzzle together?", for example). If they would, help them get started with the new activity. If they say that they don't want to do anything, ask them if they would like to do it again sometime and take them back to their room.
It sounds like a lot of work, and you may even have doubts about how well it will work, but it really does. Once the "Blitz" gets going other staff, volunteers and family on the floor become so interested in how much fun everyone is having that they come over to see what's going on and end up helping out. It's a lot of fun for everyone and you'll be planning your next one before you're finished! In fact, I recommend that you put a dementia specific Activity Blitz in your schedule once a week as a great way to engage your dementia patients.