References
Davenport: Analytic Methods for Diophantine Equations and Diophantine Inequalities
Vaughan: The Hardy-Littlewood Method
Iwaniec and Kowalski: Analytic Number Theory
A. Granville and Z. Rudnick (eds), Equidistribution in number theory, an introduction, Proceedings of NATO Advanced Study Institute on Equidistribution in Number Theory, Montreal 2005 Nato Science Series vol 237, Springer 2007.