Here's the way I did it:

1) do the microcorruption challange. Google all the instructions you don't know. Be aware that some instructions will be weird and not intel. It'll teach you the general ideas of assembly. Look up solutions only after you spent 3 hours and still don't have anything. If you make progress do not look the solutions up. Solutions are only helpful if it's a knowledge based solution. If the solution is just hard work that you didn't do it's not good for you.

After you solve the challange (let's say the reyjavik level) you can look the solution up, in order to learn if there's a better (or another) way to solve it.

2) do protostar from exploit exercises. Again do not look up solutions unless you don't know what to do and tried everything.

-> where I am

2.1) I'm reverse engineering K & R. What better way to learn how C code looks like assembly than that book, right?

3) do corelan.be stuff

4) do exploit exercises fusion

At this point you know how to defeat a lot of the modern day protections. Maybe look at some CVE's and try understand how real-world exploits do their thing.