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
Size: Don’t put too much importance on trying to perfect the size of a preemie item of clothing. There is a great difference between premature baby sizes and so an item of any size should be suitable for at least one baby. As a general guide premature babies head circumference is roughly the same as their chest circumference. The average premature babies chest measurements are 8”-14”. However clothes of all sizes are needed for preemies, so no matter how big or small your item is it will most likely fit at least one baby.
The blocking mat is another accessory that can be extremely helpful for the knitter or crocheter, or even for those who enjoy sewing and quilting. This mat serves for pinning the project to its surface, making it very easy to line up the project, keeping straight edges, hems and seams.
The charities have a lot of information on their websites, below is some general advice to help you get those needles clicking.
If you click on the resource link at the bottom of this article, you find hundreds of free patterns that will pique your interest. Under the image, Knitntyme specifies ”gauge/tension, number of stitches per 10 cm/4” or crochet hook. Suggested yarn may be replaced by yarn with a similar knitting tension.” So you don’t have to buy their yarn to download the pattern.