Sewing pins these days are usually about one and a quarter inches long, and either have a “pin head” or a glass head. They used to make pins with plastic heads but they weren’t very “iron friendly”—they’d melt during pressing.
Glass head pins are useful—you can see them easily and they won’t melt under the iron if you press with them in.
Sometimes you can find glass head pins that are only one inch long—these shorter ones are better for doll clothes than the longer ones. If you see them, grab them.
If you are going to sew with knit fabrics, be sure to pick up some ball-point pins. These will work better on knits. The ball-points easily slip between the fibres of the fabric and don't leave holes.
There are other, longer pins available these days. These are mainly useful for quilting or other applications where you need a longer pin. Long sewing pins are going to be awkward for sewing doll clothes. Also available, are all sort of pins with fancy heads. Again, having too large a head on the pin may make it difficult to use with very small doll clothes. Although, they certainly look fun, save them for your regular sewing or quilting work.
A great addition to your needles and pins are appliqué pins. These are absolutely the best pins for sewing doll clothes! These tiny pins are wonderful for weensy, awkward seams where longer pins are just a nuisance.
I use them for putting in sleeves or other difficult areas of doll clothes. They are so useful, I wouldn’t do without them!
You can find them anywhere quilting supplies are sold. Once you’ve tried them, you won’t go without either.
Whatever type of pins you prefer to use, be sure to store them in a dry location away from damp. Rusty pins will mar your work. In fact, I would highly recommend you remove pins from your work as soon as possible. Even if they don't leave rust marks, they can still leave other kinds of marks in your work. Just better to remove them as soon as you can.
If you have several different types of pins, be sure to label them in some way - unless it's completely obvious, as in the case of appliqué pins.
A great place to keep your pins is in a pin cushion.