So I'll be starting a Physics PhD program in the fall, August to be precise. Now I'm the type of person that would go and self-study whatever topic I found interesting (currently working through a reading list in GR, even though it's not a field I'm going into), but I am wondering if there are any specific topics in math or physics that are worth going into deeply that would be of any immediate benefit for a PhD accross physics disciplines. This question is mostly geared towards PhD grads or post 1st year grad students: in retrospect, what subjects do you wish you had spent time self-studying before your 1st year in grad school that would have been of practical benefit to you and your work? Ie: getting a rigorous foundation in statistics/probability, learning advanced techniques for PDE's, diff. geometry or getting a head start with Jackson's E&M? Some ideas I've thought of/already acted upon are: -picking up grad/qualifying exam problem collection book(s) and/or upper level undergrad books and working through them -Improving programming skill, something I am still working on sporadically now. Maybe find a course or project with lots of programming challenges at my level to solve? -Tutoring math/physics here and there, so that's already helping me to not forget the basics (got a few students already) -Taking apart and fixing electrical appliances around the house (done 2 and counting), maybe find an interesting diy project to work on my electronics/soldering skills (I've built a few tranny amps, I am interested in building a valve/tube amp, but not with scientific applications in mind). -I'm also looking for a job of any sort for the coming months and though I'm not picky by any means, I am keeping my eyes peeled for anything that would teach something valuable (data analysis/entry, clerical, but no luck). I've already been in the retail grind years ago and don't really think I have anything left to learn there (but would obviously take the job if I get called).