I think, the main question should be "kanji of which level of education" it is possible to learn fluently in 3 months? If to start from zero and your target is to start reading papers, magazines, and common stuff from internet, I think you have to spend not less, than 2 years to make it fluently. And you will still be confused facing some unusial readings.

The best method to learn is to write them. Just take a notebook and a pensil with a riuler, and draw lines to make neat squares about 1cm x 1cm on each page, and then start writing each kanji at least  20 or more time (some of them need to do more repetitions). While writing continue to say in your mind ON and/or KUN readings. Thus the mechanical memory of your hand and memory of your toung will help your visual memory to recognize the JI's in future texts.

The problem may be with kanji's, which have many KUN rreadings, or unusial radings of personal names. So, here may give you help flashcards.

I believe, learning kanji's is like learning a different kind of language. So, you have to run your studies like learning two languages (oral and written) at the same time. I knew people, who ignored it, and could only read well, but absolutely do not speak, and vise versa.