I like pen and wash, as I enjoy the structure the drawing gives and the freedom that delivers to use watercolour. I think it is important not simply to colour in your drawing but to add more, so that the paint and drawing add to each other.
Once I have done the pen part, I am always a little scared to start in with the colour. What is I ruin the drawing?? Having said that, if it all goes wrong, you can give the painting a good scrub under the tap and take it back to the white. It’s fine as long as your paper is good quality and your ink really is waterproof. Really you have nothing to lose by giving that a go, as you are already not happy with the result.
Anyway, I have done two pen and wash paintings from my sketches at the zoo. The toucan, I particularly like, but the giraffe I am not 100 per cent sure about. I will put it away for a while and then see what it does for me.
Here are before and after pics: