As you say that you have completed class 12th with science stream. There are many higher studies courses on which you can take admission these are as follows:

Opportunities in Medical science:

MBBS (Bachelor of Medicine and Bachelor of Surgery)
BDS (Bachelor in Dental Sciences)
B.V.S (Bachelor in Veterinary Sciences)
B.Pharm Bachelor of Pharmacy
Diploma course in Pharmacy (D.Pharmacy)
B.P.T (Bachelor in Physiotherapy),
B.H.M.S (Bachelor in Homeopathic Medicinal Sciences),
B.A.M.S (Bachelor in Ayurveda Medicinal Sciences)
Nursing (ANM, diploma in nursing, degree in nursing)
B.Sc. degree course in:

Mathematics,
Physics,
Chemistry,
Bio-chemistry,
Bio-medical,
Botany,
Computers,
Food technology,
Geology,
Home science,
Microbiology,
Polymer sciences,
Statistics,
Nutrition,
Environmental studies,
Agriculture including animal husbandry,
Veterinary science,
Dairy and poultry courses etc

Opportunities in engineering:

Computer Engineering
Electrical Engineering
Electronics Engineering
Mechanical Engineering
Civil Engineering
Agricultural Engineering
Aeronautical Engineering
Architecture Engineering
Automobile Engineering
Biomedical Engineering
Biotechnology
Ceramic Technology
Chemical Engineering
Environmental Engineering
Genetic Engineering
Industrial & Production Engineering
Instrumentation Engineering
Marine Engineering
Metallurgical Engineering
Mining Engineering
Petroleum Engineering
Plastic Technology
Polymer Engineering
Rubber Technology
Space Technology

List of important exams and options:

UPSC (Union Public Service Commission) exams
IAS
Staff Selection Board
Railway boards
The Banking Selection Boards
National Defense Academy