To prepare for RRB ALP 2019,

First MAthematics - start with NCERT 10th class book and solve examples after studying each topic and go for RS agarwal after completing this. Dont go for hard problems, level of mathematics in the exam will be medium.

Second General Intelligence and reasoning - there will be topics like Venn diagrams, Relationship questions, Interpretations, number series,etc. collect all topics and practice minimum 100 problems from each topic and learn all shortcuts for similar type of problems and more practice is needed as difficulty level can be either medium or hard.

Third General Science - You have to prepare from 10th NCERT science book , there are 15 to 18 chapters from that book you can complete 1 chapter in 2 days and after that practice MCQs and questions related to that topic. difficulty level can be either hard or medium. Make notes for this, it will be helpful when you are revising.

Fourth General awareness on current affairs - Read Newspaper daily, Practice questions on current affairs memorize important things about important topics like science and Technology, sports, culture, personalities and economics etc. After every 5 days refresh and revise your memory about Current affairs. level will be hard so work hard on this topic. 

Railway ALP exam book by LAL and JAIN - refer this book it will be useful.

All the best!