Relate the knowledge to your own life. You'll be more passionate about learning if you find a way in which what your learning directly connects to your own life You'll want to learn more if you can find a practical way to use the knowledge you've gained.
For example, you might not be all that interested in learning maths. But if you find a way to relate the principles you're learning in maths class to your fauvourite sport, you now have a reason to memorise all those formulas.