How to get mob heads effectively?

Solution 1:

I found a tutorial on the minecraft wiki that seems to be the best way to farm them. It will still take a long time, and it will probably be really hard to build and maintain but if you REALLY want the heads this is probably the most efficient way.

http://minecraft.gamepedia.com/Tutorials/Charged_creeper_farming

Solution 2:

Since Minecraft 1.13 we have Tridents. They can be enchanted with the Channeling enchantment that creates a lightning bolt during a thunderstorm if it hits a mob.

Using it thus gives one a very easy to use way to get mob heads since finding charged creepers is no longer a concern.