The two tools I use most often for sculpting are what I've dubbed my spatula. It came in a pack of three double ended plastic tools.
I use it for blending and smoothing body parts and appliques. The length is good for large areas and the tip for smaller spaces. I even use it for smoothing eye lids. I also use it to shape certain ears by moulding the clay around the end of it and I also use it to create definition in muscle bone structure etc. I find it useful because it's hard unlike a lot of the pricey rubber tipped tools, but not pointy like a knitting needle (often recommended for smoothing)
My other tool that I can't be without is actually an embossing tool. I know nothing about embossing, so I can't tell you what it's supposed to be used for but it has two little metal balls on each end and it is perfect for making eye holes, and making paw pads with. I also use it for defining facial features.
I am currently focusing on miniatures and making them to scale is very important to me.
Because of this I would have to say that along with rulers and my digital caliper my favorite tool is a Hobby Calculator at Jim's Dollhouse Pages. If you follow the directions at the bottom of his page you can even use it when not online.
It is easy to use, converts to many different scales and has been very useful to me.
I guess my favorite technique would have to be layering. I love to add things to the main piece to give it a three dimensional look.
I had not realized that until I started looking at what I have been making. Covering votive holders with clay is good, but I started adding more layers to make things a bit more interesting. More colors, and textures too. Sometimes I add some seed beads for interest and the unexpected. And I texture a lot too, adding lots of detail. It took a while for me to get here and that is half the fun of working with polymer clay.