When looking at creating a new design, one of the things that stumps me the most is understanding pull ups and pull downs and in particular if I want to add an indicator LED how would that influence the behaviour. I have certainly used them but never with confidence. I think this topic has already been addressed somewhere on the forum. So when asked what I struggle with, that comes to mind.
There is one other topic I am struggling with but this is more KiCad related and I think I will turn to that forum. It is more of a "best practice" question for connectors. I did make a comment on this on the CE Header Footprint thread.