Designers should start by asking themselves, can I eliminate or combine functions of this device? And while I can work hard with a completed device to simplify instructions, what if I designed the device with the instructions in mind?
One example: Instructions often refer to features that are not clearly identified, such as, "press release button located under the shoulder" (on this device it was an oblong button the same color as the device). Would everyone understand shoulder? How about coloring the button yellow and state simply, "press the yellow button." Simple, but effective, and with the explosion of devices coming onto the market, design is not standardized. A single patient may have to learn two or three different delivery systems.
Another example: "Push needle in at 45°- to 90°-degree angle." That's a big assumption that everyone knows their geometry. How about adding an outer collar surrounding the needle and state, "Push needle in until outer collar is completely pressing against your skin."
And provide visual or audible feedback that instructions have been followed properly. And you can add brief instructions on the device itself.
Example: "To mix powder and liquid, turn dial clockwise until it will go no further" becomes, "Turn dial in direction of the arrow until the green dots line up together."
Yes it is common sense, and simple, yet many devices today confound patients who often don't even read the manual. And you see many devices where the design was frozen long before the instruction booklet was drafted. If you approach it holistically you will end up with a device that is intuitive for the user.