The way I listen to audiobooks is right before bed or as I fall asleep. I'm busy during the day, so I can't listen to audiobooks without constantly stopping or losing focus because I have other things to do. So I only listen when I have long stretches of available time.
I go to bed and start listening till I fall asleep. I listened to 8 books last year this way. Sometimes, if the book is particularly good or exciting, I end up staying awake all night which is good and bad depending on your schedule, mood etc.
I evetually I fall asleep, so I set a timer on iPod to stop playing after X minutes so I can easily pick up where I left off the next day without scrubbing through too much stuff I already heard.
If you keep losing focus, it means you picked a bad book or the reader is not good, which is very rare for me (i'm not picky). Picking a interesting book to read is key if you want to not lose focus.