Note Taking three steps backward immediately before taking three steps forward, as instructed in some siddurs, defeats the purpose of taking the three steps forward. The purpose of stepping forward is to symbolically approach Hashem. If you step backward and then take your three steps forward, you are back to where you began and have not approached Hashem at all! 
If you do not have enough room in front of yourself to take three steps forward when beginning your amida, step back somewhat (at least a few seconds) before you say ga'al Yisrael. There is no need to take three steps back; a single large step that will give you room to take three steps forward is all that is needed.
By making a practice of taking three steps back, people have made the stepping backward part of the entire procedure, and it should not be.

Similarly, once you have finished saying the amida and walked three steps backward, wait at least three seconds before walking forward so as not to defeat the purpose of having stepped backward. Take as many steps as you need to get back to your seat--one step should suffice.