While new designers may have to rely on made-up samples, once you've landed a job be sure to obtain samples of the completed work. Add these samples to your portfolio and use to send out or give to potential clients. Build the cost of a few samples (5-20 depending on the cost of the piece and the size of the job) into your contract. For work that you feel is especially exceptional or that highlights skills you particularly want to market increase the print run by a few hundred copies and pay for the extra printing cost yourself.
Within a Reproduction of Work or Ownership of Artwork clause in your freelance design contract, include wording that specifically allows you to retain rights to use samples of the project as well as preliminary designs in your portfolio (for marketing of your business), design competitions you might enter, publications such as books or magazines (suppose you wrote a book or a magazine article... you'd want to be able to show off your best work), or other similar uses.
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