Try chilling your cake before you crumb coat, and then after. I highly recommend Yolonda Gammps' recipe for Italian meringue buttercream, it's velvety and light so it won't drag on the cake causing more crumbs.
I brush a simple syrup over the cake while its still warm, wrap it tightly and chill overnight, and brush another coat of simple syrup over the cake right before I crumb coat.
The syrup moistens the cake and as a result, very little crumbs get caught in the crumb coat. It's 1 cup water 1 cup sugar. Bring water and sugar to a boil in a saucepan, stirring constantly.
Boil for about 1 minute, or until reduced slightly.
Let cool and store in a covered container for up to a month. Use it on cakes, to sweeten coffee, or any other time you might need to dissolve sugar in something.