UPSC

Step 1: determine your mind that you are ready to give your heart and soul to it. Even ready to spend 1 to 1.5 years with reading.
Step 2: determine if you want to take UPSC coaching or self study. (My suggestion if you have your blood relation know about or in preparation of UPSC take their suggestion or go for coaching classes) and must know that institute is just for guidance and you only have to study. (Have it in mind, it helps)
Step 3: Start seeing daily news at night in Rajya Sabha TV at 9 pm from today itself. (Available on YouTube)
Step 4: Have policy of one subject one book and don't heap up books.
Step 5: thorough revision of same materials.
Step 6: test series to your capability at your convenience.
All the best.

I would suggest to choose a course based on your interest. This is the complete list of UPSC Optional subjects for civil services main examination. You have to opt for any one subject. Animal Husbandry and Veterinary Science
Anthropology
Botany
Chemistry
Civil Engineering
Commerce and Accountancy
Economics
Electrical Engineering
Geography
Geology
History
Law
Management
Mathematics
Mechanical Engineering
Medical Science
Philosophy
Physics
Political Science and International Relations
Psychology
Public Administration
Sociology
Statistics
Zoology
Literature of anyone the following language: Assamese, Bengali, Bodo, Dogri, Gujarati, Hindi, Kannada, Kashmir, Konkani, Maithili, Malayalam, Manipur, Marathi, Nepali, Oriya, Punjabi, Sanskrit, Santhali, Sindhi, Tamil, Telugu, Urdu, English. Agriculture
If you choose a course among these subjects it will reduce the time you allocate for optional subject preparation. Further you will have a clarity which will help in your interview process.

You can choose subjects which you feel interested and also can be chosen as an optional subject in UPSC exam thereby it reduces the time for additionally preparing for optional subjects. This is the complete list of UPSC Optional subjects for civil services main examination. You have to opt for any one subject. Animal Husbandry and Veterinary Science
Anthropology
Botany
Chemistry
Civil Engineering
Commerce and Accountancy
Economics
Electrical Engineering
Geography
Geology
History
Law
Management
Mathematics
Mechanical Engineering
Medical Science
Philosophy
Physics
Political Science and International Relations
Psychology
Public Administration
Sociology
Statistics
Zoology
Literature of anyone the following language: Assamese, Bengali, Bodo, Dogri, Gujarati, Hindi, Kannada, Kashmir, Konkani, Maithili, Malayalam, Manipur, Marathi, Nepali, Oriya, Punjabi, Sanskrit, Santhali, Sindhi, Tamil, Telugu, Urdu, English. Agriculture.