Organza is not the easiest fabric to work with. While it is beautiful, the fact that it is sheer means all of your seams and hems will show on the outside, not to mention it puckers easily and frays even more easily. If you want to use organza to make a lovely dress, it can be done as long as you keep a few important things in mind.
Wash the organza before you work with it. It may shrink slightly and throw off the finished garment if you don't.
Use a new 11 to 14 needle for sewing light- to medium-weight fabrics. The 8 to 10 needle is too lightweight to work with since organza is a stiffer fabric. Make sure the needle is new as it will be sharper.
Sew french seams instead of serging the seams together. This makes the garment look neater and more finished. Make the french seams as small as you can.
Use synthetic thread, polyester preferably. Organza is strong and needs a strong thread to hold it together. Cotton thread breaks too easily to hold up to organza.
Use a long stitch length. Organza puckers and in order to avoid that you have to lengthen the stitches. Each sewing machine is different and you will have to sew on a scrap piece of organza to determine how long the stitches should be.
Starching organza makes it easier to work with. Use the spray-on starch and it should wear off by the time you are finished.
Use a small amount of Fray Check, or a similar substance, before you hem. This will keep the hem from fraying so badly and will make the finished garment look better.