How to make Lilac flower cake | Italian meringue buttercream | Buttercream flower cake 

It's all about controlling the pressure while you are piping. There are cake decorating classes that teach you the fundamentals to cake decorating. If you are just starting out, then I recommend having less icing in your decorating bag at a time. I'd also recommend getting an elastic to stop the icing from moving towards the top of the bag. Another important tip for success is icing consistency... if it's too runny or loose then it'll be harder to pipe flowers... the same if it's too stiff... but different flowers need different consistency of icing... for example, roses need a stiffer consistency than the flowers in this video. Also, freezing the flowers once they are piped makes it much easier to move them onto the cake. You pipe them onto squares of wax paper, then you put them on a plate or something, and move them into the freezer for 10 to 20 minutes. Then it's easy to remove them from the wax paper and place them onto the cake without ruining them.