My first crusader, Karius, was in Knight. Instead of running or logging out every time Cariousus or Azantar logged on, I would go and either A) Attack the Nexus standard, or 
Wait for them to come attack my standard and defend.
That character was one of my biggest learning experiences, and was also the first character that I got a legitimate PK on (towards the later end of his life). However, I also got my butt handed to me by classes that no crusader should ever lose to.
A couple of general tips:
PKing
Treat every battle like a learning experience, and stop caring whether you lose. Get excited when you win, and let it drive you on even further, but don't let losing discourage you one bit. Also, it's a great opportunity to learn some great, easy re-equip spots, and decent non-rare armor that's always in. I don't know if you're a c/c, rogue, or a melee, but it is fairly easy to get some significant +hp/mana or +hit/dam with non-rares. Log every fight you ever have (get a MUD client that's conducive to this - MUSHclient has the option for a 500,000 line output buffer). Great for logging fights, if not entire play sessions, without having to remember to turn on a logging program. Rolling a new character? Read and re-read every single PK log on the forums. People often even add in little notes about where they made mistakes, or where a fight turned tides - read these notes carefully, so you don't find yourself making the same slip-ups.
Travel
If you're still having trouble, and haven't already, roll a good cleric and travel everywhere and identify everything. And pay really close attention when you're on trips - because if you're not good (or at least improving) on the role that you're supposed to be filling, then no one's going to want to take you anywhere. There have been times in the past where I've consciously decided not to invite someone to go on a Desolation trip because either A) They don't pay attention as a healer and let someone die or have a close call, or They want EVERYTHING, and get really upset when they walk away with one item or no items. Not everyone can have every uber piece of gear, so if you don't get something (or anything) that you want, don't worry about it. The best thing you can do is just ask your party to make sure that you get to ID everything. Equipment plays a pretty big role in this game, for better or worse, so learning where stuff is and how to get it is an important skill.
Mentor
Other people have already hit this nail on the head, but having an in-game mentor is a fantastic opportunity to learn more. It's one thing to have someone explain something to you via PM or over AIM, but it's another thing entirely to have them show you firsthand, or even better, show you multiple times.
Challenges
Roll a neutral character, join Battle if you're so inclined, and challenge EVERYONE. Challenging is (usually) a "safe" way to learn how to PK. You can try different tactics, and really play balls to the wall without fear of dying (or, for some people, without fear of losing your equipment). However, don't treat a challenge like a game of luck - CHANGE your tactics, SWITCH up what you're doing, and TRY new things. Otherwise you're just beating your head against a brick wall - and all that's going to give you is a concussion. However, if you're using challenging as a safe net, you have a very important restriction - the minute you kill someone at the end of a "friendly" challenge is the minute your reputation goes down the drain. Word of mouth is a bitch, and you better bet that three other people will ask that person how they died, and those people will not trust you anymore. So respect the unspoken rule of a challenge, and don't kill someone at the end of it, unless you're prepared for the backlash.
Preparation
Fighting in this game is 90% preparation, 7% skill, 2% luck, and 1% waiting for your opponent to screw up. Until you learn which ones you need for specific fights, have every spell/skill at your disposal up and ready anytime there is a potentially hostile opponent in your PK range, and ESPECIALLY if they're in your area. If you pass by someone you don't trust, don't stop and go back to look at them. Because chances are good that in the time it took you to come back, they've gotten ready for an attack, and they're going to seize the opportunity to get the jump on you if you're not careful. The only time you can fully trust someone in this game is when you're a goodie and they're a goodie. Other than that, prepare for the worst at all times.
Edit: I agree with Festy and MoP to the tune of, if you're going to fight do it on your terms and not on your opponent's. However, I will say that the only way to learn to PK is to fight every battle you possibly can. And to do that, you can't be so selective as to fight only when you are practically guaranteed victory. Especially because if 75% of your PKs are won, but you still suck at PK (IE - You consistently win fights with unprepared people, or get lucky a lot), you're setting yourself up for some huge disappointment when the tide turns and you get stomped because you still don't know how to use flight and sanctuary.
For more, check out: http://forum.theforsakenlands.org/showthread.php?t=17293
For even more, check out: http://forum.theforsakenlands.org/showthread.php?t=5337
i'll keep these in mind 