It's a nice question you have asked. First of all thanks for your patience. Hope you have gone through my earier answer related to gpsc. GPSC is the body which recruits Class I and II officer in the State of Gujarat. If you want to prepare for the GPSC. It's so easy as per my opinion. GPSC is conducting Three Tier Examination.

For a Preliminary They're selecting 6 Times more candidates for the post to be filled up. i.e. if there is a 400 posts then they will pass the 2400 people in preliminary examination. For preliminary exam there will be a objective type of questions.

Gujarati and English - 150 Marks (75-75 Each)
Maths and Logical Reasoning - 150 Marks

General Studies - 200 Marks
In First Paper Guj. and Eng. let say it Paper I, It covers entire grammar of these two subjects and For Gujarati They will also ask about Gujarati Literature like a Poet and writer of any famous Poem or essay or Short stories, Novels etc.

Before uttering about how to prepare let me tell you that for these kind of exams like GPSC, you should have a plan B in your pocket. Because GPSC isn't like other competitive exams that comes every year. And even if GPSC announce its schedule, it is never going to complete the whole process in less than 2 years. So have some other plans too while preparing.
As far as preparations for GPSC are concerned, first of all just get through the syllabus of prelims and mains thoroughly. If you are an engineering student, it will be easy to crack the prelims as it has 150 marks for mathematics and reasoning.. You don’t need to prepare topic wise for this paper. Just practice more and more question from any book.

The language paper that contains sections of English and Gujarati grammar is easiest among all.
Last paper of prelims is tricky one. Don’t depend on cheap book available in market for GS paper.

Keep habit of reading 'The Hindu'. You can get it on ur cell. Note down any imp news. No need to read monthly magazines and all. No need to read about sports too as they ask general questions. Keep your eye on every government sites. They keep updates about schemes and all.

For mains, take geography as optional. As it has minimum syllabus and maximum chance of scoring. Read NCERT's of 10-12. Main key for success in optional is write, write and write!