How to make a cheap light box
About six years ago I was given a great tip for transferring drawings you do on tracing paper or light weight paper such as Bank. This cheap light box is very cheap – in fact it is so inexpensive it is free!
After to you complete your sketch, you tape your drawing to a clear glass window or doorway. I prefer to use a southern facing window (in the southern hemisphere where I live) as it faces away from the sun. It would be the reverse if you live in the northern hemisphere.  I found if I used a window that faced directly into the sun; it was a bit hard on the eyes so I don’t recommend it.
On top of the drawing you tape a sheet of 300 gsm, watercolor paper and you should be able to see through to the drawing underneath well enough to trace over it.
You may need to add a little pressure to the paper to see the tracing underneath easily.
I use this technique if I feel I will be doing a lot of erasing on my initial drawing before I get it right. It lets me work on the tougher tracing paper and also it obviously does not damage the watercolor paper through excessive erasing.
It also means that if I then go ahead and mess up my watercolor painting – hey it happens to everyone, it does not take me long to re transfer the drawing to a new sheet and I hence save myself a lot of redrawing time. This also lets me be a lot more relaxed with my painting, especially if the drawing required a few hours of work, as it does not take very long to retransfer the sketch.
In my studio I have an A3 light box but this technique can be used for any size depending on your window!
I used to rub graphite on the back of a sheet to create graphite paper, but this cheap light box is a much cleaner and easier technique.