The charities have a lot of information on their websites, below is some general advice to help you get those needles clicking.
Fastenings: Plain flat half-inch buttons are best to use for fastening. Avoid nylon and metal fastenings, as they get very hot under the incubator heaters. Do not use Velcro as a fastening, it is very scratchy on the hook side and also damages knitted garments when they are laundered. Ease of dressing is vital for preemies and as a general rule it is best not to use ribbon as a fastening as ribbon can often be fussy to tie on a garment so small.
Other types of stitch markers on the market today can be clipped onto you project when needed, and then clipped as required. These allow the individual who is working on the pattern to come back to a certain place in the design later in the project, leading to a great deal of precision in the creation of the project.
Finally, one essential accessory to keep your equipment safe is a set of knitting needle caps, which are designed to be placed over the end of your needles when they are not in use. As mentioned above, needles can cause damage to bags that they are kept in, and can even prove a safety hazard, especially if they fall into the hands of children.
The charities involved usually have free knitting patterns and advice on their websites so do not be worried by all the details as you really will be able to find a garment to suit both your knitting skills and the babies needs