Second-order voting means that the aggregate of everyone who does it votes towards a consensus value of things being the value they think they are; first-order voting means that there's no consensus process, instead getting a double-counting of perspectives, where a post that is easy for many people to evaluate as good gets voted highly because they independently think "this is good, therefore I will upvote it". if they all instead think "this is x amount good" and vote towards that, then it reduces incentive towards popularity contests and the stuff that is harder to evaluate but good stands out better.

I'm much more likely to take existing karma into account when strong voting. For weak votes I'll just vote my opinion unless the karma total is way out from what I think is deserved. This comes up mostly with comments that are bad but not so bad I want to beat the dead horse, or that express a popular sentiment without adding much. 

If you want Karma to be about more or less of this on LW, then the first strategy seems to match that.  And adjust (removing or reversing your vote) if others vote to the level you think is right.

I think there's enough others on the site that #2 tends to happen, regardless of your intent, so maybe don't worry much about that.

In fact, don't worry much about any of it - karma is lightweight and noisy, and it's a mistake to treat it as a particularly fine-grained signal.