There isn't really a 'proper' method for connecting two switch stacks together.
My suggestion is to use at least two links across both switches in the stack and aggregate them into a port-channel.
However, please ensure you read the release notes for your switch version. There are some known issues around cross stack port-channel. Eg.
- Cross-stack LACP bundles experiencing a switch reboot will cause the remaining online port to experience an outage of up to 30 seconds. The same is seen again when the switch comes back online (present since MS 10)