Advice on covering a cake with royal icing, please!

[ttalloo]

I need to decorate DS2's birthday cake today, with royal icing that I've bought from the supermarket, and as I'm not using marzipan, I don't know how best to apply it to the cake to avoid getting crumbs everywhere.

I've got some leftover buttercream from the filling of the cake, so I was wondering whether I should smooth that over the cake before putting the royal icing on.

Any advice would be much appreciated!

I would glaze the cake first with some melted apricot jam, possibly...

Do you mean royal icing? That's the one that sets hard. You smooth that on with a palet knife? Suspect you mean fondant though, so butter cream will do. That's what I usually use.