Serial voting describes a pattern where your votes seem to focus on specific users instead of posts. If you up-vote a question and a bunch of answers to it, then you probably don't have much to worry about.
This can be a little tricky in very niche tags where you tend to see the same people answering most of the questions and you notice that the majority of your votes tend to go to the same people over time - this is perfectly okay too, as long as it's the posts you're voting for. After all, if all you see during the day happens to be COBOL and Fortran, who are we to judge what you vote for?
We're evaluating a change to the system that would send you an inbox notification if the system detected that you were probably casting a few too many votes for friends or coworkers, and provide links to information on why that's bad for the system overall. Taking very niche tags into consideration has made progress there a bit slow, but we're close to coming up with something that should work reasonably well. As others have said, if the UX doesn't at least give you a hint that something might be 'bad', then you've got a problem with the UX if people continue doing it.
All in all, if you're honestly voting to give what you feel is better information more prominence in the system, then you're probably okay. If you have any other motivations, then you're probably going to see votes reversed and perhaps contacted by a moderator.
Don't worry so much about evaluating what you're doing in the context of systems designed to thwart bad behavior, just worry about the real motivation for what you're actually doing :) Systems get smarter and more forgiving where appropriate over time, so don't waste too much time trying to avoid them.