1) Use pen and paper and/or graphviz to find most pleasant/understandable layout. It's may be not that obvious.
2) Use vector graphics editor (Adobe Illustrator, Inkscape or CorelDRAW) to draw by hand.
I always thought there must be some special tool, way better than Draw.io, OmniGraffle and everything, but just vector graphics. Maybe quiet some work.
1) Use pen and paper and/or graphviz to find most pleasant/understandable layout. It's may be not that obvious.
2) Use vector graphics editor (Adobe Illustrator, Inkscape or CorelDRAW) to draw by hand.