Hi there are plenty of institutes that coaches in classroom, provide distance learning coaching and online classes like AAKASH,ALLEN etc,you have plenty of time, and if you work smart, you can really score well easily with or without the aid of coaching institute but i would suggest you to use some form to guide you, i will tell you how to prepare for both AIIMS and NEET,

Physics and chemistry- physics is considered one of the toughest subject for medical aspirants,but very interesting. choose any good book of your convinience, there are plenty of good books as many mentioned already. read the concepts thoroughly,understand them cover to cover, if you have doubts, clear them then and there. solve atleast 300 to 500 questions per chapter, check ,analyse and rectify your mistakes. solve again. the more you solve the merrier.initially you wont be getting many correct answers, but as you keep on doing am sure you will see your score rising. solve previous question papers too

Biology-aiims doesnt cover most part from ncert like how neet does, in neet around 300 marks are from ncert text book itself, so u need to thorough ncert first and then read any good book of your choice and solve as many questions as you can

General knowledge and current affairs(AIIMS only)- read newspapers regularly, keep yourself updated always, use year books, they ll help you alot.

Joining a coaching institute or to prepare through self study totally depends on you. To crack NEET exam your concepts shold be clear. o give edge to your preparation go through previous year papers to understand the exam pattern and level of questions. Focus on important topics you can solve MCQs related to important topics for your practice.

You can also solve complete mock test series to understand your strength and weakness. So, you can work upon them.

All the Best!!