Before you read...pre-read each chapter! It takes about 15-20 minutes, but is definitely worth it!

How to pre-read:

Glance at the timeline (how long will it take you to read this?).
Read all boldface subtitles as you flip through the chapter.
Look at maps, diagrams, tables, and photographs, and read the captions.
Read the colored inserts - they're interesting!
Read the summary at the end of the chapter.
Read the questions at the end of the chapter too!

While you read...active involvement with the material is key! Do something while you read. Here are some ideas:

Highlight
Enumerate the chapter
Write out the questions at end of chapter and answer them as you go along reading
Take notes on the theme you've been assigned (music, art, literature, architecture, or technology)

There are no magical solutions and there is no substitute for reading! Textbook reading takes hard work and time...so plan for this!