National income accounting is the grammar of Indian Economy. Every Economic Survey chapter, every Budget speech and every RBI policy statement uses words like GDP, GVA, real growth and the deflator. Learn them once, precisely, and the rest of the subject becomes readable.

What UPSC asks

Prelims: definitions and identities: what is included in GDP and what is not, factor cost vs market prices vs basic prices, GDP vs GNP, nominal vs real, which body compiles the data.
Mains GS III: growth versus development, the limits of GDP as a welfare measure, the quality and credibility of statistics, and jobless or uneven growth.

Key sub-topics

Sub-topic	What to master
The aggregates	GDP, GNP, NDP, NNP and how they connect
Valuation	Market prices, basic prices, factor cost; product vs production taxes
Methods	Production (value added), income and expenditure methods
Real vs nominal	Constant prices, base year, GDP deflator
Institutions	National Statistical Office (MoSPI), release calendar of estimates
Beyond GDP	Per capita income, HDI, green accounting

Start with National Income Accounting, then use the quick revision sheet and practice questions.