To add to Jon's comments.
Avoid topics people feel strongly about. This basically means most things subjective. The reason being that you'll earn downvotes just because people disagree with you.
Downvotes received when you're below the daily rep limit are fine. Later upvotes will cancel them.
Downvotes received when you're at the daily rep limit are potentially a problem because order suddenly becomes important. 5 upvotes then 1 downvote is net -2. 5 downvotes then 1 upvote is net 0.
Downvotes received when you're above the daily rep limit (due to bounties and accepted answers) you want to avoid at all costs because they always count and future upvotes (that day) won't counteract them (unless you drop below the daily rep limit). So if you're at 230 for the day and then answer something that gets 40 upvotes and 10 downvotes (this can happen) you'll go down to 210 for the day.
As for bounties, avoid any the will be decided between midnight and midday UTC. Of course the bounty starter may just decide early at some random time but often people seem happy to let them auto-pick an answer. Also if someone is active between midnight and noon UTC to start the bounty at that time then it's not that unlikely they'll pick the answer in the same time frame 5-7 days later.
Answer C# questions. There are the most of these, giving you the most room for earning rep from accepted answers plus it seems likely that you're more likely to get votes from these due to a larger audience. Some tests of the SO dump would prove this one way or the other.
Answer quickly and answer well. Most votes come in an initial burst. If you need proof of this consider Why are many of the banking sites implemented in Java rather than .NET?. I answered this 2-3 hours after the question was asked. At the time I believe the next answer down was at +15-20 votes. I think in the next day both answers improved by 5-8 votes. This answer has been an exception to the normal rule in that it is a "slow burn" (meaning it continues to get votes over a long period of time) but the point is it took a long time to counteract that 2 hour head start.