Generally a good rule of thumb is also the golden rule, do unto others as you would have done to you. Basically if you would not like being stood up on a date, or being lied to, it probably is a good idea not to do these things to others.
Always show respect for others, respect and trust are the foundation for a good, long lasting relationship. If you do not respect the other person, you will probably not treat them as they deserve to be treated. Since people do not like being mistreated or looked down on, your relationship most likely will not last.
If you do not trust the other person, this as well can lead to problems. Trust is paramount for a proper relationship since if you can not trust them, then how can they be considered a friend or a lover?
Relationship edicate extends beyond simply showing respect and trust. Like all forms of etiquette there are various things you should observe. Just as you should use the proper fork at a fancy restaurant you should make sure to abide by social rules as well.
A relationship is a give and take ordeal, you give to your friend or lover, and they give to you. But you need to know when to give and when to take, since like with everything else there is a time and place. If you give too much you can come off as overbearing and make the other person uncomfortable.
On the other side if you take too much you can come off as selfish or needy and this will just drive the other person away. It requires proper etiquette to know how to moderate yourself properly and to achieve the right balance.
Compromise is another thing you should keep in mind. Not everyone sees eye to eye on every little thing. Compromising is what allows most relationships to work. One of you may want to see one movie, while the other wants to see a different movie. You could compromise and agree to watch one movie now, and then watch the other movie next time.
If you can not come to an agreement that can lead to resentment since it looks as if you are simply selfish and always want things your way. Sometimes it requires one of you to step up and admit defeat. If one of you does that, the other will probably follow through.
It takes two to fight so as long as someone is the bigger man (or woman) and simply goes with the flow it can make things run a lot smoother. However that does not mean you should always do this, as I said it is a give and take, if you always back down then they take while you give. Both of you have to give in once and a while.