When I was in University, I spent 4 years working part-time at a Baskin Robbins. With time, I learned to decorate cakes and this wonderful tip when filling the icing bag.
I make up the icing in a bowl and then pull out a rectangular piece of plastic wrap. Then I add icing to the middle. Proceed to fold over the plastic wrap, leaving a small opening at one end for the icing to go through and twist off the other end.
Then, you drop the icing into the white icing bag, with the opened side going in first. It's ready to go. When you run out of icing, you just pull out the emptied plastic wrap and pop in a new bag.
A LOT less mess and easy to use. Good luck :)
Do you have any good tips or techniques?
Send them to me at oomelement (at) gmail (dot) com and I'll post them.