I made my first two layer cake today (yes, still very basic I know). I let it cool for an hour after coming out of the oven and then crumb-coated it. So far so good. I colored my remaining icing yellow to ice and then started covering the cake. Tons and tons of crumbs on the sides (the top is fine. What did I do wrong?
If you use a very thin layer of "crusting" buttercream, it will hold all the crumbs together and they won't get in your final layer of icing. Maybe it wasn't a "crusting" buttercream recipe?
After applying the crumb coat, let it crust. You can also put it in the fridge for a little bit... just enough to make the crumb coat harden up. Then you can apply your final layer of icing (I use the Wilton Icing Tip), and it seems to work out fine. Hope that helps. Maybe others will have some suggestions for you. Hang in there, it does get easier with time.
My habit has always been to bake the night before a cake is due. I never crumbcoat or ice sooner than 8-12 hours after baking. The cake is very fragile for a quite a while after it is baked. When I take my cake out of the oven, I put the pan on a rack and cover it with paper towel for 10 mins. Then I remove the paper towel and level the cake in the pan by slicing off the crown. Then, after replacing the paper towel, I flip the cake out onto the rack. Next I cover the top and sides with saran wrap, and place the pan back over the cake.
The saran wrap never completely covers the cake which would trap all the moisture and could encourage bacterial growth. The paper towel allows some moisture to escape so the cake won't be soggy, but will still be moist. The cake cools on my kitchen counter about two hours (or till completely cool) and then the cakepan/saran wrap covered cake, still on its cooling rack, goes into a covered plastic storage box until the next morning when I will crumbcoat or ice. First, brush off any loose crumbs before you start. Your cake will have firmed up and stabilized and you'll have an easier time working on it. Prepare your cake as usual and get going 
This method has worked for me for 20 years...and 2000 cakes.
you can brush crumbs from your cake with a pastry brush before crumb coating.
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