Finding a co-designer
Many celebrated games are co-designs, and pairing up can transform a stalled project. A good co-designer brings skills you lack (maybe you invent mechanisms and they excel at balance and math), doubles your playtesting capacity, and keeps the project moving when your motivation dips. The catch is that a co-design is a small business partnership, and it should be treated like one.
Co-designers usually emerge from working relationships rather than want ads. The designer who keeps giving you sharp feedback at your local design night, the person whose prototype you loved at a Protospiel, the regular you trade tests with on a Discord server: these are the candidates. Before proposing a full partnership, collaborate small. Ask them to help develop one subsystem, or co-design a quick contest entry, and see whether your working styles fit.
Settle the business questions in writing before serious work begins, while everyone still likes each other. Who owns the design? How is credit listed? How are royalties or crowdfunding proceeds split (an even split is the common default)? What happens if one person stops contributing or wants out? A one-page signed agreement covering these points prevents nearly all co-design disasters. Handshake deals fail exactly when the game succeeds.
Also agree on how decisions get made. Some pairs give one person final say, others require consensus, and some divide domains (one owns mechanics, one owns theme and content). Any structure works if it is explicit. The co-designs that collapse are usually the ones where nobody ever said who decides.
Video tutorials
Finding the right mixture of luck and skill with Richard Garfield
10 Types of Board Game Designers (And How to Discover Your Own Style)