I use my favourite lightweight knit fusible. In the trade you'll have the luxury of getting a whole roll of fusing sliced up into lots of convenient rolls, but at home you'll need to save all your scraps of fusing and cut them yourself! Layer them up to save time, and cut them into lengthwise strips along the grain, about 1.5cm wide.
Here I'll demonstrate fusetaping an invisible zip. I do this to all zips on delicate fabrics for stability and reinforcement, and all zips inserted into a side seam to prevent the bias edges stretching. This is how I did it on my Skirt #108 Burda 1/2010 that I've just completed, and I also applied it to the zip edges on the yoke which were curved. Simply press the fusetape onto the wrong side along the stitching line of your zip, extending 2-3cm beyond the zip notch.
Then overlock any seam edges, and sew your seam up to the zip notch as if the fusetape wasn't even there.
Then insert your zip as normal. You will find that the base of your zip is much stronger, and it will be easier to sew in your zip too - now who doesn't want that?!
Fusetape is also really useful in preventing loosely woven fabrics from 'grinning' when the seam is strained - which is not a nice look on the CB of your skirt! Just apply fusetape to your seamline before stitching and your seam will be strengthened.
Hope this helps you - and happy sewing!