How to more effectively read papers? I just started my Ph.D. and am trying to participate in a couple reading groups. Often, these groups will cover 2–4 papers a week. Upperclassmen seem to have no issue staying up-to-date and informed, but it typically takes me 2 hours minimum to digest a paper and probably something like 3–4 hours to really start grokking the equations. How can I read papers more efficiently?

I assume part of the answer is just practice. After a while, I will get faster. But are there any habits I can form now that will help?
Simply continue reading papers and going to your reading groups.  When you first start graduate works (which includes reading papers), it feels overwhelming.  When you first start, 2 hours isn't uncommon.

A couple of things I learned about reading papers

1) Quickly read through each paper first (to get an idea of what is presented), then read it more carefully.

2) Print it and write questions in the margins.

3) Give yourself a set amount of time to study each paper.  Once that time is up finish noting down things you do not understand and move on.  Bring your questions to the reading group.

4) By "upperclassman" I assume you mean students that have been studying for their PhD for a while.  If possible, arrange to read the paper with one of these more knowledgeable students.  They will be able to guide the inevitable self study you'll need.