verb
BAD : I was preparing myself to go to bed when the phone rang.
DUBIOUS : I was preparing to go to bed when the phone rang.
GOOD : I was getting ready to go to bed when the phone rang.
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If you prepare yourself ( for sth ), you get yourself into a suitable mental or physical state for something that you expect to happen: 'Relatives of the victims were told to prepare themselves for a long wait.' 'The villagers are preparing themselves for further flooding.'
When you get ready or prepare to do something, you make yourself ready to do it: 'The company is preparing to expand its European network.' 'I had my breakfast and got ready to go to school.'
Note that get ready is very common in spoken English and is often used in connection with the simple things that people do as part of their daily routine.