Short answer: Build a static GK base once, then add monthly current affairs and revise in short notes.
Static GK
Use a single book for static topics and revise it a few times.
Current affairs
Use a monthly compilation or trusted news source and keep brief notes. Prefer recent editions.
Revision
Revise weekly so facts stay fresh.
Frequently asked questions
Should I buy yearly current affairs books?
Prefer recent compilations because older ones go out of date.
Can I sell old compilations?
You can, though demand is better for recent ones.