One day it will just click mate, we all have to sit down and work out stuff sometimes, sometimes, anyone who works with mutiple relays will be no stranger to doing this. Sometimes we get called to faults and you may have to draw stuff out to try and work out the previous electricians and logic
I expect everyone has their own unique way of learning things, but I use the same method telectrix mentioned above, follow the path of the live, I always used to tell the apprentices to imagine it's a pipe with water flowing through it, follow it through the switch contacts and up to the light. If you reach the light then it will work if you don't, it won't.
Another tip when drawing wiring diagrams out for 2 way switching, it's easier to follow if you draw to switch contacts in by that I mean a solid line between com and L2 and a dotted line between com and L1 so you can trace over the different switching positions.