To get the swirled looks of the purple and pink cupcakes above, you need to use a large closed or open star tip (try a number 1M or 1C).
One thing to note - if you're using sprinkles they often adhere better to the swirled frosting as they can settle between the swirls. If you're using cupcake toppers then I like the smooth frosting look.
I think my fav overall so far is using the 1M (like the purple cupcake).
One thing I have noticed is a lot of bakers I see on TV and cupcake shops that carry "fancier" cakes use the 1A (like the green cupcake), but for some reason it looks like poop to me! haha.
Another method I've seen a lot lately (which someone recently called "couture style") is not frosting all the way to the corners of the cake like this:
I don't think I really like that, not sure. Looks kinda naked dontcha think?
Playing with the different tips is certainly fun and you can create some neat designs (if you have the patience) so have at it!
Again, how does this NOT look like poop? heehee....


