Are there any rules of thumb I should know about when modifying the
line-height of text?
As a general rule of thumb, as the font size increases the
line-height can decrease. We usually want to use line-height to establish a good vertical rythm on our body copy first before adjusting the line-height of our headings.
Line-height usually ranges from 1.35-1.85. I recommend applying a line-height of 1.5 to your body copy just to establish point of reference. You may want to test and adjust this value to establish a vertical rhythm that is best suited to your particular font face.