Focusing the preparation keeping the syllabus as the base would help you save time as well as your can have your attention on the important topics
Clearing the basics being studied in class 11th and 12th is the key to score great in the AIIMS 2015
Practicing as much you can from the past year question booklets and from the sample papers available in the markets can help a lot in understanding the format and get along with the questions that can come in the same format in the exam.
Increase the speed by solving the maximum number of questions in a day. For instance if you are able to solve 80-100 questions in a day with ease increase it to 140-150 in a day after a week, this can boost your confidence as well as let you have a planned preparation for the final exam.
Practice as much you can on the difficult areas and keep asking the doubts to your mentor or even friends but make sure no doubts shall be unanswered.
Make the separate notes of all the formulas of physics and record the chemical formula and reactions of chemistry.
Prepare the diagrams of biology as you can expect such in the exam to identify from the given diagrams
As biology is a subject of theory make sure you take out time on everyday basis to revise the definitions and meanings of the terminology you learnt.