It would be better if you could go through the below provided link as it has preparation tips along with important topics and books as well which you can follow as these will be helping you to go in a right direction -

All about Civil Engineering preparation 2018

Hope this helps!!!

Below are the recommended book sfor your preparation

Engineering Mathematics-

-Discrete Mathematics and Its Applications by Kenneth Rosen

-Higher Engineering mathematics by B.S. Grewal

-Advanced Engineering Mathematics by Erwin Kreyszig

Structural Engineering-

-Theory of Structure by CK Wang, S. Rammamrutham, L.S. Negi & Jangit

-Theory of Elasticity by Timoshenko & Gere

-Theory of Structure by Wilbur & Norris

-Strength of Materials/Mechanics of Structure by Gare & Timoshenko,

E. Popove, L. Singer,

-B.C. Punamia, Rammamrutham

Geotechnical Engineering

Soil Mechanics by Gopal Ranjan & Rao,Venkat Ramaiha,S. K. Garg,

B.C. Punamia, V N S Murthy

Water Resources Engineering

-Water Resources by S K Garg

-Water and Waste Water by SK Garg 1 and 2

-Fluid Mechanics- RK Bansal and Fox and Richard

Transportation Engineering

-Transportation by Justo Khanna

Environmental engineering

-Environmental Engineering by S. K. Garg Part I & Part II

-Waste Water Engineering by B. C. Punamia Part I & Part II

Geomatics Engineering

-Surveying (vol. 1,2,3)  by B.C.Punia, Ashok Jain, Arun Jain

You can also refer below article to know about more details about the placement

Best Books for GATE Civil Engineering

Good Luck!!