I've been having a look at some different styles of sketching and what I like about each style. One book I read recently was Ray Evans' Travelling with a Sketchbook. He has a very loose style, which at the same time catches a surprising amount of detail. He is conversely also really good at hinting at things in the middle and background with out doing too much detail there. I've had a go at trying to catch that level of detail, while moving stuff around. 0.05 Staedler black pen. I learnt that this type of sketch takes a very, very long time to do!