Mark posted about this maybe two or three years ago, but we seem to be regressing and he told me it's ok to post a reminder.
If you take the time and effort to answer a question, then the strongest likelihood is that it's worth an up vote. After all, why not? When the OP returns the next day to see some answers and they see they have accrued rep, they will rejoice and this may help push down our drive-by rate.
When I look at the 'new' page, or sometimes the 'active' page, I like to look at questions that have received up votes first. Perhaps others follow the same pattern or perhaps not, but a question with up votes will attract viewers and that gives your stuff more exposure.
I know there are corner cases out there where you can write an answer and not up vote the question because it doesn't qualify, but these are rare and some of what we have shows a great answer to a great question and the person answering didn't up vote.
I expect Mark will be along in due course to explain more about why up voting questions is good for the site. In the meantime, please be reminded that once you input your answer to pause and consider awarding an up vote to the question.
Adding after Mark's comment: And Tweet your stuff too!