Hii,

If you want to prepare for a civil judge then you can take coaching from several institutes. If you want to start early then you have to put your main focus on subjects like the law which is the main subject and  English including some knowledge of computer also. Since in the prelims you'll be having three papers of these subjects. English is asked at an intermediate level whereas basic questions come for the computer.

You can go for some books by authors like M P Jain, K.D. Gaur, Avtar Singh, etc.

Hope this helps.

All the best!!