From QM to QFT learning approach The passage from the undergraduated course of quantum mechanics and the first course of qft was plenty traumatic: usual concepts like the hamiltonian of a system with its energy eigenstates, orbital angular momentum, the uncertainty principle and so on seemed to me vanished in this new framework. Moreover, some unanswered questions from the undergraduated course like the decay of an excited electron into the ground state with a photon emission still remained obscure. During the past months I was able to link something, but it's more like of having a big hole from the last section of NRQM and the quantization of fields. Furthermore, our QFT courses mostly focussed on scattering theory and renormalization, which is good, but left so many topics behind. So what I'm asking you is if there is a book, or a collection of books to follow for closing all these gaps in my knowledge. I know that this sounds like the nth-related post on QFT books, but I tryed many of them and they seems all so "self referenced". For example, Maggiore is like a short summary of the state of the art, Srednicki is good if you need to check something but you dont need to go deep, Schwartz seems to have forget what does it mean to learn from zero this subject; Zee offers some hint, but it misses this "bridge"-like behaviour which I'm asking. The only relevant book I think it's made for that purpose is Weinberg, but for a newcomer it seems rally unreadable with all that ugly and gory notation. Hoping to get answers and good advices and that this post will be useful for people like me who are trying to understand QFT beyond the LSZ formula.
Edit: so as far as I can understand, first of all I have to go through a good book of RQM which doesnt simply show me all types of relativistic eqs. Then I should turn to the first 5 chapters of Weinberg and "lose" time over them to get solid foundations. Then I can go for I&Z to get the feeling of the qft mindset. Given those, I should be able to appreciate better the books I have cited. If anybody else wants to share his/her experience it would be appreciated and welcomed.
 A: Your curriculum committee was evidently complacent.
The gap is only there if you fail to take the bridge course after your QM course.
Generations, including mine, had that gap filled by J J Sakurai's classic Advanced quantum mechanics ISBN-13: ‎ 978-8177589160 . The book  shows you the nuts & bolts   behind all this  pompous/abstract verbiage of QFT, and speaks the language of the generation that invented the stuff.
Also the 1964 classic Relativistic Quantum Mechanics, (junior partner to the much more famous QFT sequel  "v II") by  J Bjorken and S Drell.  Generations of teachers knew it by heart, and assumed everybody did, so they skipped words, a habit picked up by those who wrote subsequent QFT texts.
A: From my point of view, i.e as a graduate student still studying QFT, what you are experiencing is comepletely normal - in the sense that you cannot expect to get a full understanding of QFT and its relation with QM on your first course. I think you will even realize (to me at least it seemed so) that even from the QM point of view alone, your undergraduate course isn't enough as a basis for a true understanding of QFT, a much more profound knowledge of QM is necessary for QFT. It is safe to say (at least to me) that those gaps you talk about maybe won't be filled at your first approacch to QFT. To me it's a learning process that is still going on, where with time and patience different pieces comes togheter. The best approach to me is what you are doing, following your classes and get some more informations from textbooks.
Some books  which I used for specific topics are the following (the main path was given by my professor's lectures). During my first approach I used Maggiore, and Mandl and Shaw, which gave me a general understanding of QFT and some tools for calculations and physical understanding. Then I used for specific topics Weinberg (es all chapter 2) and Peskin. A big step to get a sense of QFT to me is truly understanding the LSZ reduction formula, and according to my professor this is well done in the original paper and in Bjorken and Drell (we mainly follower their approach).
Another helpfull resource are the lecture notes by Timo Weigand, these to me are great as an introduction. On more advanced topics I am using Cheng and Lee book which seems really good (But not as an introduction) and other books for specific arguments like Strocchi's work on SSB and non perturbative aspects, or Schwartz for aspects regarding the Standard model and its phenomenology. The point to me is not to focus on a single book, but on the arguments - try following your lectures using the textbooks that suit you as support, to get a better understanding. You will see that some textbooks explain better some things and pass on others, so mixing is fundamental to me. Slowly the formalism becomes clear and you start to see what kind of reasoning is proper in QFT, and from here there will be many questions that will spontaneously arise, leading to more formal aspects which helps understand the theory and its limits better.
