Unless you’re a talented graphic designer, then you’re going to need the services of a pro. Rather than using a separate service, you’ll find that using a printing service that also offers a talented design service is likely to be far more cost-effective. Ask to see previous print run examples and discuss expertise with your potential print partner before deciding if they’re the right one for you.
Of course, they should be accredited to the highest of industry standards. Examples include the internationally recognised ISO 9001 Quality Management System certification and the colour guarantees provided by ISO 12467-2:2013 certification.
Choosing a provider that has a great track record in top-quality design, combined with industry certifications provides a good baseline from which you can fine-tune your printing partnership requirements.