Subject to a voltage, a dielectric elastomer can deform substantially, making it a desirable material for actuators. Designing such an actuator, however, has been challenging due to nonlinear equations of state, as well as multiple modes of failure, parameters of design, and measures of performance. This paper explores these issues, using a spring-roll actuator as an example. We formulate the equations of state with two degrees of freedom and describe the constraints due to several modes of failure of the elastomer, including electrical breakdown, electromechanical instability, loss of tension, and tensile rupture. Also included is the compressive limit of the spring. We show that, for the spring-roll actuator, loss of tension in the axial direction will always precede electromechanical instability. We then describe a procedure to maximize the range of actuation by choosing the parameters of design, such as the prestretch of the elastomer and the stiffness of the spring.