Now that you have a fair idea of what illustrators do, let's paint a picture of their roles and responsibilities for you:
Communicating with people from various backgrounds and learning to portray concepts from their points of view. A prospective client will give you a 'brief', which means they will tell you what they expect you to do. You will have to ask as many questions as possible to understand what they want and create your sketches accordingly. Say you're sketching a cover image for a children's author. You need to understand the story, the image your author wants, and a style that your author and audience are comfortable with.
Working on initial sketches or 'scribbles'. Before you begin a detailed sketch, you should ideally create a rough sample or scribble to share with your client. This will help you get their views before finalising your illustration. Ideally, before you get into the scribble stage, discuss your ideas with your client and get their views so you're both on the same page.
Figuring out your niche and developing your talent accordingly. There are so many styles and fields within illustrations to choose from! You need to figure out which one works best for you and hone your talents in that niche. Say you're really good at creating cartoon animals for children's books. Wouldn't make sense to take up medical illustrations then, would it?
Learning traditional as well as computer-aided design techniques. You will have to be well-versed with both forms of designing, and use the technique that is best-suited to the project you're working on. You may choose to use both techniques or either one, depending on the brief given by your client or your personal preferences.
Finding new, unique ways to illustrate technical designs. You will have to work on more serious projects like medical or technical illustrations from time to time. While you will have to make sure the organ you're illustrating is accurate, you can always find a style that makes it look appealing.
Working with different sketching tools. Your sketches will involve pencils, watercolours, poster colours and more, depending on your brief or your personal style. You should be good at using all these tools.
Negotiating money and time in your favour. You will need to develop this skill to make sure you are getting your worth. If you're working as a freelancer, you will have to understand basic business management.