It took me a while to figure out china painting with pens. Youtube did not help but showed how to waste paint. I use the 2 to 1 linseed-mineral drying oil mix in the active painting pallet to dampen a brush. The brush is used to transfer paint to tip of pen by painting the underside of pen nib. Holding the pen at 15 to 25 degree angle seems to work best. Clean pen using a paper towel to rub off paint.
If the ink work from pen appears faded when it is put on try swishing the brush in the paint and re-load the pen again.
I found a 102 pen nib works great for fine lines and use 107 nibs for fine "hair lines".
Extra nibs should be ordered for when you drop the pen. Now that I own extra nibs I will probably never drop the pen again but they will wear out.
Sometimes the pen will stop working even though it appears to have enough paint. I have found hitting my wrist on table while holding the pen down will get the paint flowing again.
My current brushes are narrow Royal Soft Grip Brushes made of red sable and Taklon. I use an angular brush size 1/8 inch for most of my work. The Taklon brushes last longer than the red sable. Both provide good coverage and I can not tell the difference in final results. They are easy to hold and affordable.
A mug or cup support for painting can be made with a narrow board sticking over the edge of the table. Use a second board for a hand rest leaving a gap for the cup to be painted. Slide cup into narrow board and rotate cup as needed to paint all sides of cup. It even works for vases and teapots.
A clean brush may be used to reduce paint to provide a fading appearance.