I want to quit government job and join private job. What to do?

Please remember that a bird in the hand is worth two in the bush. So don't quit a government job without getting another job. This is my first piece of advice to you.
Then coming to change of job, there are many ways for that.
1. In your present organisation, if there is any job suitable for your M.Tech qualification, apply for that. Even though immediately if there is no vacancy also, they may consider you as an internal candidate for a suitable job. I suggest you meet your HR head or boss and explain to him about your qualifications and make a request. I know people who changed their jobs in this way even some government offices and government undertakings.
2. If the present organisation is not having any suitable job in your line of education, you can apply for other government jobs through the proper channel. You have to look around for various government notifications and if any suitable job vacancy is announced you have to apply for it through the proper channel.
3. You can upload your CV to job portals like naukri.com. They will be sending you alerts if any suitable vacancy is available. You can also browse the site and search for suitable jobs and apply for them.
4. You have to see advertisements in various newspapers and apply for them
5. India Study Channel job section is also a useful site for you to know about the opportunities both in the government and private sector.
6. There are many private placement services whom you can contact. But don't pay them any money. You can get your resume registered there.
Whatever may be the case, you should not resign from the present job, till a pucca offer letter from some other government or private organo]isation is there in your hand.
Once you lose your present job, it will not be possible to you to get back the job. If you feel necessary to apply for an eligible long leave and try for a new job.

I would not suggest you take a risk of relinquishing your government job so easily without the proper verification of the private job for which you might be interested. In this context, I would advise you to look into my suggestions prior to taking up any final decision regarding the switch over-
1) You should contact your personal department highlighting the fact that you are M. Tech but due to unfavourable situation, you took up the clerical job. Your personal department might help you to meet some boss of the technical department and make a good impression on him.
2) If there will be requirements of the internal candidates in the technical sides, you might be offered such a job suiting to your qualification.
3) Since the government job is more secured and stable, think twice prior to leaving the same.
4) You may look out some job consultant established in this line such as Naukri.com for better job opportunities in some private sectors with better perks but ensure that such a job is secured.
5) Once you are offered such a job, verify internally to what extent this would be promising to you.