NPPL
The NPPL ground examination subjects are:
§ Air Law
§ Principles of Flight
§ Communications (see the 'Radio' section of this site)
§ Navigation
§ Operational Procedures
§ Aircraft General Knowledge
§ Flight Planning & Performance
§ Human Performance & Limitations
§ Meteorology
You can study them in any order. I have ordered the above list in the sequence I might suggest – but it is personal preference indeed you could study several at once.
How long does it take? Some people take two years and some have done it in two weeks. Self teach is the traditional way but you can also get help trough structured courses, one-to-one coaching and 'apps' see below
NPPL SLMG SYLLABUS v4 17 Feb 10 from Andrew Oct 2013.pdf
NPPL SLMG Syllabus
NPPL Flying Skills Test.pdf
Summary of Syllabus
NPPL New Currency rules.2.MC.doc
NPPL currency rules