Here are  a few suggestions you can always have a look on:-

The written exam is a must which comprises of a written test, a medical exam, a personal interview & then the merit list. The exam pattern for RRB consists of general science & technical ability, general awareness, arithmetic, general intelligence and reasoning.

science section:

General Science for Indian Railways RRB Exams -ALP/Group D/NTPC/JE Railway To The Point General Knowledge and General Science from KICX Objective General Science from Expert Compilations Lucent's General Science by Ravi Bhushan RRB: Senior Section Engineer from Ramesh Publishing House Encyclopedia of General Science from Arihant Experts.

Technical Ability section:

RRB Technical Exam by Dr. Chandresh Agrawal RRB Technician Electrical (Grade-III) Recruitment Exam by Dr. Lal & Mishra Railway Technical Question Bank by Kiran Prakashan

General awareness section:Lucent's General Knowledge from Lucent Publication Pratiyogita Darpan from Upkar Publication Manorama Yearbook by Malayala Manorama 

Arithmetic section:

Arithmetic by R. S. Aggarwal Quicker Reasoning Test from Upkar Publication Verbal & Non-Verbal Reasoning by R. S. Aggarwal.