Make stuff. Be prolific about it. It doesn't have to be good. You just need to put it up so that you have some visuals to talk through your design process. If you can't explain why you made the decisions that you did, then keep working until you can.
Sell your ideas. It's not enough to just create and upload. You have to convince people that your ideas are good. Do it through blog posts, case studies, or presentations. Whatever floats your boat. Believe it or not, this is equally -- if not more -- important than actually doing the design.
Be well informed. You need to know some history of design and have some opinions to argue both for and against trends or styles. Quote a design book you've read in an interview. Use an example you saw in a design documentary. Knowing the space allows you to have intellectual conversations about design with like-minded peers at networking events and interviews.
Find creative hobbies -- whether it's photography, illustration, calligraphy, watercolor painting, or pottery. Doing artistic stuff keeps your creative spark alive. The cross-pollination of art and design is where some of the best work comes from. Use your design skills for problem solving and use the artistic hobbies for self-expression.
Network! You won't like to hear this, but it really is all about networking. Reach out to people via email, follow influential designers on Twitter, and try to attend local design meetups. Having a pleasant conversation with another senior designer is sometimes all it takes for them to drop your name into the referral bucket of their hiring department.