Dear student,
The minimum qualification required for admission into a diploma course is passing tenth standard/equivalent examination, with at least 35 percent in science and maths subjects.There are various entrance tests also for admission to the diploma programmes offered by various polytechnics of a particular state. These are some of the diploma courses you can choose from:

• Diploma in Automobile Engineering
• Diploma in Computer Science & Engineering
• Diploma in Electronics and Communication Engineering
• Diploma in Mechanical Engineering
• Diploma in Aeronautical Engineering
• Diploma in Information Science
• Diploma in Civil Engineering
• Diploma in Electrical Engineering

You haven't mentioned any particular polytechnic college in which you would like to take admission. Please mention it so that we can help you further.
However generally first you need to find out that whether a college admits students to diploma courses on merit basis or conducts entrance examinations. Then you need to fill the application form when it is released. If it is merit based admission, then a merit list will be announced after few time, you have to get your documents verified and then pay the fees. If the admission is through entrance examination then you need to appear for it and rest of the process remains the same.