Haha, ok. Well this was written in a hurry so I hope it's not too shabby

Your closest friend I might be
throughout your journey's course
though you can't always find me
when ruled by other force

Through me you power may grow
your mind may expand too
and although you might not know
I know you better than you do

So you can talk to me at will
or order me around
you'll find me on the small hill
with three lines on the ground