How do you get yourself to actually finish a book instead of losing interest within the first chapter?

If you lost interest by the first chapter, than I don't believe that the book you are reading is for you. 

If it is something you must read for work or perhaps studies, try a group approach where you and your coworkers/friends/classmates are reading it together. Create a way to push each other, maybe a little competition where the last one should buy the rest coffee. 

Read the introduction prior to purchasing, the topic should interest you and you should finish the book within2 to3 weeks and not keep extending the period for in the end you lose interest and forgot what you've read earlier