If you've read my previous negotiation posts (here and here), it's easy to get the impression that I see negotiation as an adversarial encounter. The truth is negotiation does not exist in a vacuum, but within the context of a relationship.
The four types of negotiations are
low stakes, low relationship:
This is something like two strangers deciding who will enter an elevator first. There's no relationship at stake, and nobody particularly cares about the outcome. Just decide these quickly and move on.
low stakes, high relationship:
This is where you are dealing with someone who you want to maintain a connection with (or at least not annoy), and an outcome that doesn't matter that much. An example is who would pick up the tab for lunch (unless you've got expensive tastes). Anything that seems fair to both parties is fine here.
High stakes, low relationship:
This relationship may be short-term to nonexistent, such as selling a house. In these cases, getting the best possible outcome (ethically) will be the priority. You can pull out all the stops here, almost.
High stakes, high relationship:
These are the most difficult types of negotiations. The relationship is as important as the outcome, but both will have a large impact on your future. If you are discussing your starting salary with a prospective employer, it does not make sense to poison your relationship over a few dollars. In cases like this, it is important for both parties feel like they have been treated fairly by the other.
One concept that helps in these scenarios is win-win. In other words: how can both sides get as much of what they want at the same time? The key here is to focus on what matters most to each group. The prospective employer may be willing to pay more if the candidate can start immediately. A candidate may be willing to take less pay for a more flexible schedule. These kinds of trade-offs have to incorporate something other than the pay, so they work best when there are multiple variables to talk about. It's even more important to know yourself and your opponent as much as possible, beyond the BATNA.