One of the most important parts of drawing ultra-realistically is using the right tool at the right time. I mentioned using the right paper in a previous post, and the differences between charcoal and graphite in another. In the image here I use a 6B charcoal with different types of blenders to show the different effects. In a future post, I'll show different erasers.
The top is the blending stump - tightly wound soft paper with points at both ends. You can use the point or the side to blend, and they come in a variety of sizes. I use the smallest one the most, because I can get into very small areas with it. To keep it clean after use, just drag it backward on clean sandpaper, rotate and repeat until you have a clean point. I use blending stumps for fur or any small detail area.
Next is the tortillon, similar to the stump in that it is rolled paper with a point. The paper is a little rougher and it is less tightly wound than the stump, and tortillons have only one pointed end. Cleaning and sharpening is the same, with sandpaper. I just recently found these are great for penguin feathers.
Paintbrushes are a unique tool for charcoal work. I have two in my pencilbox: one with a typical round tip and one with a flat angled tip. I used the latter in the image because it is firmer. The round-tip brush is softer and has a very gentle effect. I have used paintbrushes by dipping them in charcoal powder and applying it to the paper for smooth areas.
The chamois leaves a very smooth texture, but it does pick up a lot of charcoal, making the area much lighter. I like to use chamois for backgrounds mostly, and for applying charcoal powder to the paper in large areas.
Finally I like the tissue for smoothing out backgrounds. Put a thick layer of soft charcoal and blend in circles with the tissue. Tissues don't pick up as much charcoal as the chamois, so the area stays darker. Use plain tissues, not anything with lotion or antibacterial whatever in it.
Don't use your fingers for blending. While it is a common practice, the oils from your fingers will get on the paper and change how the charcoal looks over time. In fact, I do my best not to touch the paper at all, even holding it with cotton gloves when I need to move it to keep from getting fingerprints.
I find it takes a lot of experimentation and even a bit of intuition to find which tool will work best in a new situation, and I'm always on the lookout for new tools to use.