We've been looking at this very notion in class.
It is also helpful to look at the nature of each character's personality and the way that they react to various occurrences.
For example, in the opening scene, would it be realistic to portray Ghonerill and Regan as ugly whitch like women and Lear as a bumbling old man on the verge of senility???? Also how do you depict the relative evil of characters such as Regan and Ghonerill. Furthermore think of how you would depict the relationships of characters as you perceive them. For example, if you think that there is something unnatural about the overboard love of Regan and Ghonerill for their father how do you portray that???? My friend suggested having the two girls sitting on their father's lap with big fake grins, almost an incestual setup.
Anyway, there's some ideas and thoughts, hope it helps!