IOS – iPhone 5 and MacBook Air take quite a few attempts to tether

I had the same issue with my 2011 MacBook Air with Lion, and I think it had to do with having changed security preferences on my preferred wireless network. I went to System Preferences > Network > Advanced > WiFi and deleted all existing Preferred Networks, then re-added them. So far, so good. It joins my preferred network automatically after awakening from sleep mode.

Actually, this is what happens for hotspot.

If there is no active WiFi connection, and you're not in the screen that says "Personal Hotspot", it turns off WiFi hotspot feature completely.

To connect your FIRST device, you MUST be in that Personal Hotspot settings page.

After that, it won't turn off until the last device is disconnected.