Depends on the type of party, how many you have to do, clients likes etc.
There are many cake decorating ideas. You can use biscuits, sprinkles, chocolates, fondant, etc. I usually use sprinkles to decorate my cake because we can buy them based sprinkles for serving our purpose of baking and they are available easily. A few days ago, i made Halloween cake, and i purchased Halloween themed sprinkles from fancy sprinkles, they were amazing.