so this is some tough love coming to you in this post. i would imagine you should expect many more years of similar tough love in a PhD program:
your first "homework" assignment as a researcher is to do some research to find what you are looking for. You made it into a PhD program so you know your way around a library.
all kidding aside... thats probably not the answer you are looking for, but more often than not at is the answer you are going to get in academia at your level with such an open ended question...
what kind of research do you do and your research interests?!
someone who does content analysis for a living is going to have a different idea of what is helpful and what makes a good paper vs. someone who makes models that predict the coupon redemption rates of somali immigrants. things become very specialized and fragmented which is why you begin to learn how to answer your own questions. because, frankly, thats what research is about.. also...writing a good research paper starts with conducting good research first --- and that really is a culmination of synthesizing just about everything you've learned (and will continue to learn) up to this point.
seriously though read the first few pages of a bunch of books and check out the few that you like best. also your professors should all have a long list of both required and suggested readings that you should consult.. this will be the most relevant to what you are studying.
seriously, just start reading and find your own way. in many ways you are on your own now. that is my best piece of advice for you... you will identify writers that you like and you will start to figure things out based on that. it will take time and lots of effort so hold on to your hat and start buying coffee in bulk