Our answers would be relevant if you could let us know our city, ability to travel, affordability.
1.There are many cricket academies in major cities run by or have an India national player on the board. Choose an academy that has coaches or open talent day wherein you can display your ability and the experts will identify your strengths and weakness. You can enroll for a 3 month - a 1-year program based on your circumstances. For instance KIOC, Bangalore offers 1-year program for weekends (Rs 17,000/yr) to One year two sessions/day (Rs 30,000/year) (http://www.kioc.net/)
2.Since you are 18 and keen to play for the country, try your luck with the IPL teams close to your city that has coaching too .(http://www.delhidaredevils.com/dd-academy/)
3.National cricket academies are functioning in Bangalore, Delhi etc wherein you can enroll yourself. Depending on the city you can choose from some of the well-known academies in India.(https://www.collegedekho.com/articles/top-eight-cricket-academies-in-india/)
4.With the IPL going well, most teams have their own fan base or supporters group.Try and get in touch with one of the brands, this would open doors for contact with players, reserve players, coaches etc (https://www.royalchallengers.com/boldarmy)
5.What are your plans for graduation and higher education? Give a thought for at least a degree that can help you for further employment and a career. Something to fallback if cricket chances become slim.