Decorating cakes refers to texture and color mostly. If you want to make a soft cake, you should use only fruits or other soft products like gelatin. If you want to make it chucky you should use hard caramel for decorating cakes, strong bits of chocolate or other crunchy products.
Decide on how you will decorate your cake. It helps to draw it on paper or have a draft especially if you intend to make a complex decoration or you have a theme in mind. These days, cake decorating does not only involve the usual floral and decorative borders has gone into decorating real flowers or having 3D decorations of some baseball or camera or designer bags that are also made out of fondant or icing and can be eaten along with the cake. In fact, some designers even went beyond making the usual square or round ones but into those that resemble designer bags, or cameras or shoes, or some cartoon characters.