You completely immerse yourself in some books (e.g. War and Peace) and take short dips in others.
Some are better read during flights or short breaks. Others require close attention with ballpoint and pad nearby.
For some odd reason, I've found that immediately picking up a second book shortly after completing another does not do justice to the second book. Why? Because you have not really finished the first book. It's still working away on your mind. Take a 24-hour break.
And never fall into the old trap of feeling that you need to complete a book. If, after two or three chapters, you sense the book isn't working for you, move on to another book.
After 24 hours, of course.
Fill the in-between time with magazines.