There are many ways to get lots of karma, but the most effective one is writing good answers that are "hearted" by lots of students.
Here is a list of all the actions you can take to get karma: socratic.org/karma
An important thing to note is that every time someone hearts your answer, you get points. If you are the only contributor on that answer, you get 100 points for every heart. If there are multiple contributors, you get a percentage of the 100 points that corresponds to how much of the answer you wrote.
Imagine how many points Ernest got from hearts on this answer.