While I'm sure my technique is not perfect it works for me. I don't have any super fancy cake decorating equipment, only what you'd normally find in the kitchen. I learned quite a bit from my darling, he says icing the cake has a lot to do with wall spackling. Believe it or not he also iced a cake for me when I lost it.
How to Ice a Cake with Buttercream
Baked,Cooled, Filled Cake and crumb coated cake, chilled
Large round piping tip
Spatula or Pastry Scraper
Paper towel/kitchen towel, slightly damped
Cake Turntable (I use a non fancy Lazy Susan from Ikea)
Crumb coat is the first very thin layer of icing that you smooth onto the cake to seal in the moisture and all the crumbs. Chill the cake after you crumb coat it.
1. Place the crumb coated cake onto the turntable (I use a cardboard underneath of each of my cakes for easier handling)Ice the cake with buttercream using a pastry bag fitted with a LARGE ROUND TIP
2. Using a spatula or bench scrapper start smoothing the cake sides, turn the turntable as you go. You'll have excess icing on the spatula, that is normal, just scrape it off and wipe the spatula with a clean towel. Continue until the sides are somewhat smooth, holding the spatula so there is a 90 degree angle between the sides of the cake and the turntable.
3. Smooth the top by pulling the edges towards you with the spatula.Wipe the spatula in cold water and continue, keep turning the turntable.
4. As you see in my previous step I didn't use enough icing, to cover the side up to the top. That is to show you that it is okay, not perfect, but okay, mistakes happen. I corrected them, I applied more icing and smoothed the cake again so it looked like this.
5. Once your cake is smooth, chill it then smooth out little imperfections. I use cold water to wipe my spatula as hot water causes butter in the buttercream to turn slightly yellow.
6. Before you move your iced cake onto the cake board chill it and then using a spatula lift it up carefully(remember to use a cake cardboard round underneath the cake), pipe a large dot of icing in the middle of the cake board and place the cake directly on the board. Dot of icing will keep the cake in place on the board.
Here is a neat trick I used to decorate the cake. I used a bottom opening of a large piping tip to make a piping guide.
7. I used dark chocolate ganache to pipe the rounds around the cake.