As a goalie I never have to pay close attention to blue lines and the offside rule. Staying onside is something I only ever have to think about the rare time I play other positions. Coach explained that I need to remember to not enter the offensive zone ahead of the puck, and when in doubt "toe the line".
This photo captured a good example of that situation - almost offside, fallen down and tangled up in another player's stick, not sure where I am but with a toe on the line to keep myself onside. It's probably the best move I've ever made while playing on the forward line.
Coach was very proud of me, and happy to see that his very patient coaching paid off. When I crawled to the bench he patted me on the head and explained that I was actually on defense, and in my own zone, so I didn't have to worry about staying onside.
Being a goalie is much less confusing. I only have one line to think about, the goal line, and I just have to make sure no pucks get across it!