T+MMM -- Techonology, Money, Marketing and Management
Could be skills found in 2, 3 people too; early you wear multiple hats.
Look for complementary skills; don't need three managers at the start; don't need three engineers.
Test your prospects, like dating for marrage. Can do "the thing" that's in their skill-set in "T" time? eg: I'll get the landing page built in 2 hours I'll get our legal paper work in order this week I'll get some ads running on $SITE and get 1000 clicks I'll get three meetings with investor prospects.
Startup events can be a great way to find new people outside your existing network. Eg: Startup Weekend - Real or Virtual
Alignment
The Founders are all in for a long journey together, must have good alignment. Do you want to build the same size / type of busienss (eg: SMB vs VC Backed)? Do you have the same exit stratgey? Do you envision the same type of growth (steady vs hyper) Can you make the same time commitments
Tools
Use an Equity Calculator