How can a graduate student most efficiently become an expert at his research topic? Taught courses typically do not reach research level, so there is a significant gap in knowledge that has to be bridged by a graduate student in order to make meaningful contributions to their field. What is the most efficient way to bridge this gap? I could come up with the following possibilities:


Find advanced textbooks, prove all the theorems [if maths] and do all the exercises yourself.
Organize seminars with other graduate students with related interests
Go to conferences or talks given by staff about their research


Is this list exhaustive or is there anything I missed? Which methods of learning are recommended in which situations?

For definiteness, by 'expert' I mean the level necessary to understand current research articles and (in principle) independently reproduce the calculations/proofs.
For most disciplines, advanced textbooks still provide, albeit necessary, foundations. Conferences allows you to hear what is new and is as such a good way to know where fields are going. I am not sure what you mean by seminars but discussing new papers and topics is always a good way to advance knowledge. But, the major point is to read up on published papers and to focus on the topic of your thesis. The point of research is to advance knowledge and this means you will, or at least have a chance to, be an expert on the field you are researching. So in my view none of the activities 1-3, or combinations, make you an expert, only your own sweat over publications and own work will do so.