The most popular proposal is to encourage AI researchers to think about "Friendly" AI, to program morality into their potentially self-aware code and to generally take measures to ensure that any intelligence that they create will be benevolent before it's turned on for the first time. The problem there is that professional AI researchers don't have a monopoly on the technology. Given the numbers, it's more likely that someone who isn't a recognized researcher will create a generally intelligent computer program before a major research institution will. And what then? Unless there's some way to compel every hobbyist and grad student to program a certain level of friendliness into their experiments then all of the warnings and precautions will be for naught.
With known existential threats there are warning signs. If someone is developing a deadly virus or building a dirty bomb they'll most likely have to order specific materials and use certain lab equipment. There will be red flags that someone who is looking closely might have a chance to see. But with a computer program? All someone needs is a computer. Maybe dozens of computers, or more likely dozens of cloud servers hosted with several different companies. If we took this threat very very seriously and tasked a government agency with stopping potentially harmful AI, it would still be almost impossible to catch in time. For all of the famous people sounding the alarm, what solutions are available?
The threat isn't very likely, and unstoppable even if turns out to be real. All we can do is focus on the AI problems that we can solve, develop existing technology and try to chill. If there's one thing human intelligence will always be good at, it's hoping for the best.