What are you frosting it with? If you are just now putting on the butter cream, I would suggest getting a pan of boiling water going, stick your spatula in the hot water. In a few seconds it will be warm, take it out dry it, and then smoothe your frosting. If the butter cream is already crusted over, take a smoothe paper towel (no pattern on it, the brand Viva works well) and place it on any rough spots and either smoothe with your fingers or fondant smoother. Hope this helps
Kate
OH!! Go to the articles, look at the upside doen cake method. I had the same problem this fixed it permenant
The upside down method is great for getting the tops of you cake REALLY smoothe, but for some reason I have trouble getting the sides to look good. The look smoothe but when you step back they are slanted. I try really hard to keep my blade as vertical as possible but I'm still having a heck of a time. I went back to using an offset spatula and it worked better. I'm wondering if getting one of those pastry scrapers would work better. you know the ones that are square that usually have the wooden handles?
I've heard of people using scrapers you get at the hardware store too. I think it's what you use to fill in nail holes. It would be with the painting supplies.
Personally I use a plastic bowl scraper I got at my cake decorating supply store. It was under $1.00 and is this plastic, square thing, similar to the pastry scraper below.
Other Ideas
Look at what she uses.
http://www.cakecentral.com/article46-Step-By-Step-3D-Cake-Sculpting-Baby-in-a-Flower-Pot.html
Or a pastry scraper (Ikea has a nice one for around $3.00)
http://www.boscovs.com/webapp/wcs/stores/servlet/ProductForm?storeId=10001&find_spec=26967&productId=379673&langId=-1
I went to Home Depot and got a plastic drywall knife to smooth the sides. I haven't had time to use it however but from everything that I've read on here that should do the job. Probably next weekend I will try it. Will be going to a party for the firehouse and you guessed it yours truly got nominated to bring dessert. What a surprise! So I will try it then and let you know.
One word, VIVA .. I use Viva papertowels and a crusting buttercream icing .. Once I get my final coat of icing on the cake, I let it sit for about 15 minutes, then I take the smooth side of a Viva papertowel (if they are printed.. if you can find plain white, you can use either side) and lightly rub the cake with your hand to smooth .. you do the sides the same way.. once you get the knack of doing this, you can get your cakes so smooth, the almost look like fondant 
haha Misdawn! You know me too well I swear by my Viva papertowels! Couldn't make it without them! lol
You may try adding a little more confectioners sugar to your icing .. I'm not sure which recipe of buttercream icing you use... I use one that was given to me by a lady that owned a bakery and taught us through a leisure learning class at a local university. The recipe is 2 cups of Crisco, 1 two pound bag of confectioners sugar (sift), 4-6 tablespoons of warm water and 2 teaspoons of flavoring (almond, clear vanilla, butter or whatever you want to use). This recipe will crust really well.. I know some recipes call for butter, which I want to try out and haven't done yet .. I've never had any complaints w/the recipe I use.. most people love it and I get repeat orders so it can't be too bad lol .. it is very sweet though, but has a nice enough taste 
VIVA are the best. My family knows that if they touch my VIVA towels, there will be a price to pay! 
They better grab a hand towel or those .69 cent paper towels I bought NOT FOR MY CAKES!!!!! I love it!
I am all for VIVA paper towels.....Gotta Love them
Denise
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