Sewing clothes for babies can be a lot of fun; since there is less tailoring to be done, they're small and cute, and can be done more quickly than typical clothes. However, there is some care that needs to be taken with clothes for babies, making sure they stick up to the wear and tear of drooling and chewing that babies routinely do.
Get some basic information on the baby you are sewing for. Ask about weight, length, and percentile of each as well as head size compared to other babies. Compare this information to your pattern when deciding what size to make your garment in. Decide the functionality of the garment. Make outfits for formal events such as holidays or weddings more customized to the baby's size. Make casual clothes roomier, so that the child can grow into them and get more use out the the garment.
Decide on the fiber content of your fabric. Check with the parents about possible allergies or sensitivities to fibers such as wool. Make sure that the fiber can stand up to abuse and repeated washings. Choose natural fibers or blends that heavily rely on natural fibers, as they are more breathable and better for a baby's sensitive skin. Select fabrics that are appropriate to the season you are making the garment to be worn in.
Take out your pattern and read through the instructions before beginning. Lay out the pattern paper on your table and cut out your pieces in the size you have chosen. Iron your muslin and lay flat on the cutting table. Pin your pattern pieces. Trace the shapes with tailor's chalk, including all marks on the pattern pieces, including grain lines and tabs. Cut out the number of each pattern piece as specified on the pattern. Baste together. Make any adjustments for fit that you may want to make here, such as length to a dress or a pair of pants, or longer sleeves. Make notations of any changes on your relevant pattern pieces.
Iron your final fabric and lay face down on the cutting surface. Pin on your pattern pieces. Trace the shapes with tailor's chalk, including all marks on the pattern pieces, including grain lines and tabs. Be sure to mark any alterations to the pieces you decided on in the muslin stage onto the fabric at this time. Cut out your pieces, making sure to include the specified seam allowances in your pattern. Pin together in the order specified on the pattern, baste, and then sew together on the machine.
Make sure that your stitching is as firm and even as possible. Double check every seam to make sure that it is securely locked and that any loose threads have been trimmed. Add notions, such as buttons, velcro, or zippers. Make sure that these are all securely fastened, and that any extraneous notions such as ties or other attachments can stand up to large amounts of stress and tugging.