don't memorize shit. try to understand it thoroughly and the best way to do that is to try and explain the subject to ur friend in a very comprehensible manner.

Study, revise, do questions, revise,revise

Relax then don't meshemded just feel it and imagine what you read

Start from forming questions and reviewing summary questions. When you read to answer questions your concentration will be improved.

Try to enjoy it as a fiction or interesting book you like to read. Don't try to force it while reading.