Laurie from my sewing class asked me for some pointers on working with stretch/knitted fabrics so I've compiled a little list.
Hope this helps!
Any questions at all, just let me know?
There are many different weights/types of knitted fabrics. Here's a very brief overview:
Single knit: Single knit fabrics are made from a single layer of thread loops. This forms a distinct right and wrong side to the fabric. Single knits are generally light to medium weight and very stretchy
Double knit fabrics are made by interlocking two layers single knit thread loops simultaneously. The resulting fabric looks virtually the same on both sides. Double knits are generally medium to heavy weight, sturdy fabrics with minimal stretch.
Most of the really stretchy knits include some synthetic fibre content to give the fabric strength and good "˜rebound' after it has been stretched. Knits are available in 100% cotton and 100% synthetic fibres, and many blends in-between.
Preparation work:
Cutting out stretch fabric can be tricky as it is so easy to stretch it out. I recommend laying out a sheet of tissue paper under the fabric and pinning onto that. It helps add a layer of stability and makes cutting much easier.
Make sure you follow the grain line (parallel to the selvage/fold line) on your pattern to make sure the stretch is going to be in the right direction. This will make sewing the pieces much nicer.
When cutting, make sure you use super sharp scissors too as the fabric can drag or be stretched with a blunt pair.
Sewing:
When sewing a stretch fabric it's important to use a stretch ball point needle in your sewing machine rather than a regular 'sharp' needle. Ball point needles have a rounded tip which allows the needle slide in between the 'loops' of the fabric (and stops cutting/fraying of the fibres) 
Use a polyester thread rather than a cotton thread as there is more stretch in synthetic fibres and will work with the fabric better.
Have a play about with some scraps of your fabric to get the best stitch length. I suggest trying a medium length straight stitch or a narrow zig zag. The bonus of the zig zag is that there is more 'give' and this will allow your seams to stretch a bit when you are wearing the garment.
You can buy a special presser foot called a 'walking foot'. This isn't essential for sewing but can give more uniform results.
Make sure you keep the edges of the your pieces even as you are sewing them . I find it helpful to pin across the fabric and stitch over the pins. This stops your 2 layers from moving around and prevents one layer being stretched more than the other when sewing. Take your time with stretch fabrics. Try to keep your pieces on the table (rather than hanging off the edge) the less pressure you put on the fabric the more likely you are to sew it well!
Good luck, don't be scared, give it a go!
