Publish and promote the job
First of all I try to find as many talented people as possible and thus publish the job on a number of sites. Considering that most engineers already have a job you need a little luck to run into someone that is currently available or will be soon.
When I ask the really good candidates why they’d consider switching job the most common reason is: the startup I work for ran out of money.
To maximise visibility I post our jobs on Angel.co (free), Stack Overflow (paid) and our own website. In the past I have tried a number of free and paid services and this is what came out on top.
Reach out to interesting candidates
In addition to incoming applications I try to reach out to engineers in startups or environments in my network.