What I like to call the hypnosis method is simple. First, raise your follower's happiness levels very close to the maximum. Then, leash followers to the pit. You'll notice the animation's changed, and the pit won't produce any unhappiness! As long as you keep your happiness levels high, you can sacrifice followers with zero consequences! Getting your happiness levels that high could be tricky, though, and you'll most likely have to invest gems into this strategy.

This one is simple and well-known. First, completely erase the Astari from existence. There are loads of guides on how to do this, so I won't bother covering it. However, once you do, happiness means nothing! Now you can sacrifice as many followers as you want and get gems galore! I recommend sacrificing any converted Astari first, because they produce 3 gems when sacrificed as opposed to the normal 1. Of course, this requires a lot of effort on your part, though.

Very sorry for the short guide, but these are indeed the only truly effective ways to get gems in Godus at the moment. You can get gems from other sources, though. List:

1. Chests. Each chest has a chance to contain 3 gems instead of a sticker.

2. Voyages. One particular voyage (the name escapes me) has around 30 gems total you'll earn from it. Other than that, voyages won't earn you gems, sadly.

Wait, that's it? Dammit.