Pink Mandala Pen Drawing

I'm really enjoying learning how to draw these Mandala 's - I'm slightly addicted - although they started off pretty bad - I do feel I'm getting better everyday. I started with the Zentangles and quickly moved on the the these, I love the way they look especially on black paper.  Its really challenging going from drawing on the PC to using pens and freehand too.  I'm starting to get the shapes the same sizes now, starting too  I'd appreciate any tips or tools that people use.