To begin, you probably already have some sewing scissors. Most people have sewing shears for cutting out patterns pieces from fabric, as well as thread snips or embroidery scissors for snipping threads. Although I’ve seen a lot of sewers use their large cutting shears for snipping threads, I find that awkward. I prefer embroidery scissors myself—they have fine blades that let you get in close and snip off fine thread in small areas.
In addition, I find tailors points are handy for trimming seams, clipping curves, or performing other small cutting jobs while you sew. They are a lot easier to use than shears, again because they are smaller, have pointed tips, and will do a neater job. You can easily get into small areas to clip or trim with a good pair of tailors points.
Besides these common types of scissors, I like duck-billed scissors, used by quilters and appliqué sewers--they're very useful for close trimming on hems and seams. They will fit in underneath one layer of fabric and trim closely without damaging the fabric beneath that. In fact, they are almost essential for trimming when you sew on lace. They allow you to get in very close without clipping anything you didn't mean too. And, of course, they are so handy if you use any kind of appliqué on your doll clothes.
Besides these various types of scissors, a quilter’s rotary cutter is very useful for cutting out small items like doll clothes. Often, you can get more control with a rotary cutter than with your big shears. Get one that has a one-inch blade or smaller. If you use a rotary cutter, you will also need a decent rotary cutter mat - these are essential to avoid cutting the surface of your table. Get the "self-healing" type. If you take good care of your cutting mat, it will give you years of service.
Another type of scissor you may wish to add to your arsenal is a pair of pinking shears. They used to be standard in any sewer's work basket back when. Swing-needle sewing machines that could do a zigzag stitch weren't common before the mid-twentieth century. Even at late as the mid-century, zigzag sewing machines weren't really that common. And they were very expensive! What did sewers do? Well, pinking shears were the answer. Either you had to hand overcast all your exposed seams, with needle and thread. Or, for everyday items, they used to use pinking shears.
Since dolls are especially hard on their clothes, pinking shears may provide an easy seam finish that definitely has no bulk. So consider adding a pair of pinking shears to your sewing scissors collection.