Any tips to get people really engaged from the get-go? Should there be a warm-up period?

Is there any tips that you can get people really engaged from the get-go? Like I was thinking about starting to bring people in a week or two weeks prior to my challenge to kind of just warm them up. Cause this last time Facebook ads got hung up and basically that day, I did it the day before people got in. Facebook ads got approved. I had 400 people in the group and then I started the program. So I think there's maybe a warm up period?