Design A Specific Paladin Code
The paladin's code, mentioned on page 63, states that paladins must retain a lawful good alignment, and act honorably. And while the book gives some general examples, like respecting legitimate authority, helping those in need, and punishing those who harm innocents, it's important to talk to your DM and nail down the specific tenets of your code before the game gets started.
This might sound unnecessary, but it's important to make sure you and your DM are on the same page regarding what standards you expect to be held to, since your code essentially decides whether you get to keep your powers. For example, you are supposed to respect legitimate authority. You are also supposed to punish those who harm innocents. What happens if you are in another nation, and you see a lord beat a slave for no reason? Do you respect his right to do that, because the laws of this nation declare it is legal, or do you take the lord to task, and free the slave of the inhumane bonds he was put under?
There are all sorts of ways you can look at this situation, but if you nail down the specifics of your code beforehand, complete with order of importance for each vow, then there will be no argument. For example, your paladin might have a descending order of priorities, with, "protect the innocent," at the top, and, "respect those in authority," somewhere near the bottom. In this case you, and your DM, have agreed that protecting the innocent, and freeing slaves from their bonds, take priority over following the laws of a nation.
There are dozens of ways you can do this, from creating your own code based on the gods or philosophies your paladin follows, to taking real world codes of conduct like chivalry or bushido and applying them to your PC. Whatever you choose to do, though, it needs to be done in concert with your DM so you are both on the same page regarding what rules you have to follow.
Decide Your Temptation
Are You An Organic, Or Sworn Paladin?
When people picture the paladin, they tend to imagine the knight in shining armor. And, because our image of the paladin is so closely tied to crusading knights, we tend to assume they have similar backgrounds and training. Years of practice with sword and shield, devotion to holy principals, and they have been anointed by priests to act as the hands of the church.
That is one way to play the class, but it's far from the only way.
Nowhere in the paladin class description does it state that you must be a member of a holy order. It doesn't say you have to even be a member of a church. While you're capable of wearing heavy armor, you could just as easily wear studded leather and fight with a longbow. The assumptions we have about the image, and the origin, of the class tend to narrow our focus so that every paladin looks and sounds like a Templar.
However, it is possible to play an organic paladin. These are people who have not been officially recognized as an agent of a church. They are adventurers who simply choose to do the right thing, to fight for righteous causes, and they have been selected by the divine as the carriers of power. In many cases, these characters may not even think of themselves as paladins; simply as blessed warriors who are doing their best to fight for what's right.