Hi Dear.

If you want to prepare for Navy exam by self study I'll recommend you to start with getting familiar with exam pattern and syllabus. For this purpose you can look for past year paper pattern. The basic area of study consist of Applied science, Quantitative aptitude and LR, GK and English. For applied science preparation clear your basic concepts of all the topics and try practicing questions. For English and GK keep reading newspaper and update yourself with current affairs and general awareness. Quants and LR requires a lot of practice on a consistent basis. You can refer to following books for your preparation:

1) Arihant Publication book

2) Lucent general science

3) Lucent english

Hope this helps.. good Luck