I am currently sitting my PPL exams (five down, two to go) and have found practice papers an essential part of my revision, not because I want to "scrimp" on the learning, but for the simple reason that multiple choice exams are typically designed to catch you out. So, even if you know the syllabus back to front, the way they phrase the questions can really throw you. So I would certainly recommend looking at practice papers before sitting the exam (but after reading the textbooks).
For initial reading, I would highly recommend Trevor Thoms' textbooks, which are pretty good. I've heard it said though that different text books are better for different subjects though –*this guide might be of some help:
Ground School Textbook Guide
Unfortunately I found it AFTER I'd bought my books!
As for practice papers, I have found AFE's Q&A simplifier to be an absolute gem of a book. It has three practice papers per topic and the questions are very close to what you get in the exam. It also offers really detailed explanations to answers – so you can work out where you went wrong.
I agree with Howard Long about Great Circle's apps. Lots of errors (which isn't good if you are trying to learn stuff) and they crash a LOT. Also, while it was good for air law which has short Qs and As, it is pretty impractical for topics such as Nav, and the questions were just too long to read on a phone for Meteorology. Another flaw is, they just give you the right answer, and no reasoning behind it. So not a good one to learn from. I bought the whole set of subjects and only really found it useful for air law and factors and performance.
Hope that's some help – and best of luck!!