How to avoid Meltdown, and why you shouldn't be that worried about it
Recently, a big vulnerability was discovered in Intel, AMD and some ARM CPUs. Meltdown allows the attacker to get data from the memory because of a hardware bug in superscalar processors; A superscalar processor tries to execute more than one instruction at a time to get more work done in smaller amount of time, instead of just having a higher clock speed. To make my explanation short, let's just say that the attacker can trick a Branch Predictor to arrange instructions in a way that would allow any program to read kernel memory. Of course, I'm simplifying the process to make it easier to understand; If you want to know more, read this blogpost from the Raspberry Pi Foundation or watch the video from Computerphile below.
One thing on what I can't agree with most people that talk about Meltdown and Spectre is the "You HAVE to patch yourself to stay secure" - You SHOULD, but sometimes it's not possible, as the fix may not be released by the manufacturer - look at old android phones or Core 2 Duo and earlier CPUs.
AFAIK, the patch consists of code that disables/overrides the speculation procedure, which usually saves a lot of cpu time by assuming that some instruction will return a specific value. This would obviously slow down the CPUs by anywhere from 10% to 30%, but there's another fix (which will also require a lot of self-consciousness when using a computer) that can have no negative impact on the performence.
NoScript, or how to avoid running malicious code
About that self-consciousness part.. NoScript only prevents running malicious code in your browser; Outside, you have to be careful to run only programs from safe sources, but that should be common sense to most advanced computer users.
Not a solid, future-proof fix...
... but still a good enough one as a temporary fix, or something for devices that won't get the fix. If you have an android phone that's more than a year old and/or doesn't have a big, bold text on the cover stating that it was produced by a gigant company like Samsung or LG, it's more than likely that you won't get an update. The same applies to End-of-life processors in personal computers, as manufacturers won't care enough to release patches for them.
The fix is terrible, but for some cases, it will have to do.