The charities have a lot of information on their websites, below is some general advice to help you get those needles clicking.
Many specialist knitting bags are also designed to specifically cater to knitters, with inner linings that are tough enough to resist damage from knitting needles or scissors being kept inside. Popular brands of knitting bags include methane, Namaste and Bergere de France, but there is a huge range of stylish and practical designs on the market from many different manufacturers.
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
Bonnie Babies: This charity sends premature baby outfits and blankets to special care baby units around the UK and to parents who need support. A mother who needed a way to deal with the loss of her premature child founded Bonnie Babies six years ago. Bonnie Babies makes premature clothing, blankets, and burial outfits for U.K. Special Baby Care Units and families. Their aim is to show each mother and family that there are people thinking of them and caring for them.
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.