How to tackle the bibliographic work as an entering PhD student? I'll be starting my PhD in the next fall. I already looked over the internet for advice for a beginner, even read two books on the subjects. Still, there is one point I haven't seen discussed as I wanted, it's the time and the way the student should be investing in catching up on his field and his specific topic, I'm speaking about the bibliographic part. For sure a student needs a lot of (continuous) input, but at the end he'll be solely judged on his output. From my previous research project, I'm not really confident in my way of balancing between going through articles/textbook material and trying to solve my own problematics. To be honest, it sometimes feels like a sneaky way of procrastinating: I'd tell myself that I'm still not ready to tackle my problem and that I need to make a little "detour" by existing works; and when it's done I don't feel more at ease to answer my questions. Or is it a normal aspect of research?

In my specific case, I'll be working on a quite new subject (string theory) when I only had advanced lecture of quantum field theory and general relativity; so I'm thinking about going through the canonical textbook on the subject during the summer, do most of the exercises and derivations in there (which already represents hundreds of hours invested), maybe revising some mathematical tools I need to be really familiar with. Once I'll have a general idea of the topic I'll jump to the main articles in relation to my thesis. I also know that I will be using numerical tools (Monte Carlo methods) and will need to get conformable with that. So far I only have a superficial knowledge and use of the tool.
Does it seem like a good use of my time? I already know that time and willpower are limited resources in grad school and I really don't want my desire to do well to burn me out from the beginning.
To be honest, it sometimes feels like a sneaky way of procrastinating:
  I'd tell myself that I'm still not ready to tackle my problem and that
  I need to make a little "detour" by existing works; and when it's done
  I don't feel more at ease to answer my questions. Or is it a normal
  aspect of research?


It is probably the most common way that new grad students attempt (consciously or otherwise) to avoid doing research :)

You have to remember that prior knowledge is an ocean you're swimming in, not a cup that you have to finish drinking. There's literally no way to "read all the prior literature": there's always something more. 

General reading is perfectly fine, but when you have a problem to work on, it's best to break down bibliographic research into:


what does prior work say about your problem and what's the key open question (and this is something your advisor can help you with)
Once you start thinking about a specific problem and are trying to apply some specific tools, is there material to help you understand those tools better ? 
When you're writing up, what related (not prior) work should you be aware of ? 


At each stage, read only as much as you absolutely need to, in order to avoid going down rabbit holes. And remember, as a new Ph.D student, it's not a terrible thing if you reinvent something that someone discovered before, and only learn of this after the fact. You just don't that happening at your dissertation defense :)