In order to make a cake easier to ice, especially if it is a very crumbly cake, you can place it in your freezer after you bake it. Ideally let it cool for several hours first to settle. Then place in the freezer over night. When you go to ice it the next morning it is easier to ice because you won’t get as many crumbs in the icing and you don’t have to put on a crumb coat first. Once you’re done icing it, just leave it out for an hour so it will thaw out.
An alternative is to place in the freezer for about 30 minutes, then apply a thin crumb coat, place back in freezer for about 30 minutes, then continue icing the cake.
This approach only works with a butter based buttercream or a ganache.