It's important to love the whole design process, from beginning to end. Make sure to keep updated with any changes in the industry; it moves at a fast pace. Having said that, don't blindly follow trends leaving great ideas behind. Doing design for the sake of design is not the way to go.
Sometimes you'll become overly invested in a design you're working on, so much so that you become defensive if it's criticized. Don't get overly sensitive about criticism - keep your mind open to suggestions. Just because someone doesn't like your work doesn't mean you are a bad designer.
Invest in your portfolio, and be selective in what goes in it. Focus on your best pieces, and make them as impressive as you can make them. Employers will often ask you to explain what's in your portfolio and why it's in there, so make sure you can explain why you included each piece.