This is a guide for leveling your paladin
The class
The paladin is the ultimate support class; they can buff, dispel and heal and are extremely mana-efficient. On top of this they have seals and judgments, that adds more utility to them. They also have their infamous bubbles, which can save your bacon or make you able to do that quest in a hot landing zone. In short, paladins are hard to kill and good to have on your team. Downside is their lack of (burst)-DPS.
Leveling methods
Paladins have a DPS problem compared to other classes. They have the lowest DPS in the game, so questing is the best way to go about leveling your paladin. You can grind, just not for XP (since doing quest yield so much more XP). Grinding can be done, but even then you are better off duoing with some DPS.
Whichever you choose, I highly suggest doing nothing but instances from 58-60 to gear up and get all your key quests done. Not doing so, means missing out on a huge amount of XP.
The traditional ways are:
Grinding:
Not much to say about this. You kill mobs, they give XP, you lvl. If you don’t have a comprehensive knowledge of where quests take you and which order is best, grinding is pretty fast for leveling.
It can be pretty boring, but listening to music or being on Vent/TS helps a lot. Get a rhytm going and stay in it. Take breaks when you mana up to not go completely blind 
The following is pretty good list of where to grind which mobs. It is however from a Horde perspective and you need to scroll down a bit to get to the guide If you read the whole bit, there are some suggestions for alternatives, which work just as well…if not better.
http://www.mpsgames.com/ms/index.cfm?page=topic&topicID=31653&categoryid=20&forumid=63
And the following lists some nice alliance spots for grinding. Also are some suggestions on questing.
http://www.wow-pro.com/Knowledge_Base/op=show/kid=515.html
Questing:
If you know your way around the world, this is the fastest way to level up. This is also known as gresting to some. Decent horde guides are few and far between (there are some on this site), alliance have it a lot better.
Horde – if you are horde, use Joana’s guide. That will take you from 1-60 in 5 days /played. It’s written from a hunter perspective, so my suggestion is staggering your progress in the guide by a lvl or two. Other than that, there are some (admittedly with holes in them) guides here in the strat section. An idea is to try and modify the following Alliance guide.
http://forums.blizzhackers.com/viewtopic.php?t=309717 is the text guide (thanks Bay_Cassius
http://video.google.com/videosearch?q=wow+world+of+warcraft+levels are links to all the videos (thanks sQren)
Alliance – if you are Alliance, you got it made! The following guide will quickly and easily take you from 30-60. Reason it’s 30, is because of the quests pre that are in and around the starter areas, so just level quickly to 30 and you are set.
http://www.wow-pro.com/Knowledge_Base/cat=135.html
Talent specs
First of all, you need to figure out how you are gonna level up? Do you prefer to solo all the way, solo 90% of the time or solo 10% of the time and do instances 90% of the time? If you plan on going solo most of the time, there is no need to go heavy in holy and the other way around if you plan on doing instances.
The following spec is a 90% solo spec. It focuses on improving your melee damage with 2Hers (for SOC), while also allowing you to heal yourself reliably in a tight spot. With concentration aura on, you have uninterruptable heals and your Aura of devotion gives 20% more armour, since you won’t be using shields. If you prefer shields, go with redoubt and shield specialization instead of imp. devo aura.
http://www.wowhead.com/?talent=axxuZxGz0hZVoet0c
The following build is if you plan on doing instances, where you will probably be expected to heal. It’s very holy heavy (35 pts), but with 16 points in Ret, you can still swing some hurt. This is the build I am using on my paladin atm.
http://www.wowhead.com/?talent=sExh0gstZV0xt
This is also the build that works well until you start raiding seriously, at which point you should switch to the last spec.
This last spec is focused on support and not on DPS….at all. Surprisingly, it’s less holy-heavy, but that is because of losing divine strength. It uses protection mostly for BOK and guardian’s favour.
http://www.wowhead.com/?talent=aVxhbgstVMtc0h
Gear
Again, your gear choices depend on your chosen leveling style…or your wallet. I carry two sets of gear on my pally; one for soloing/DPS’ing and one for healing. For solo/DPS play you should go for STR or AP, since you will do controlled pulls (and have bubbles) or you won’t be hit much (in a group). For heal-bot duty, go for INT and don’t be afraid to throw in leather, chain and cloth (you’ll still have higher armour than a priest).
Mana-efficiency…and gear
Paladins have the most mana-efficient heal in the game and it’s on a 1.5 sec cast too boot. Flash of light (FOL) makes you able to continually throw out small heals, so do this when you heal. Because you are casting all the tim, and you don’t have any talents to allow you to benefit from SPI, you need to go about your gear a bit different from a priest.
http://forums.worldofwarcraft.com/thread.aspx?fn=wow-paladin&t=932370&p=1&tmp=1#post932370 has a brilliant discussion on gear, which I will summarize below.
The starting raiding healadin, should go for INT to boost his mana-pool to the max. Once you start raiding and get access to better gear (lvl 60 blues and up), you should start to consider mana per 5 secs (MP5) and +heal. With enough MP5, you can virtually cast forever and with +heal you can cast even longer. Once you get enough +heal you can start to drop down in ranks of FOL and when you get short on mana, switch to lower ranks of longer casting heals, since they take more advantage of +heal and allows MP5 more time to work.
Conclusion
Paladin is a fun class to play, if you don’t mind supporting. If you want to be a tankadin, or a casting DPS-adin or a ret-noob, prepare to be met with some sceptical glances and don’t be too bent on doing it your way, since people have a tendency to type-cast…..besides, you have the most mana-efficient heal in the game, so use it!
I know paladins are a popular class, so there will probably be differing opinions on my layout of the class. This is my take on the class, but feel free to chime in below and I’ll add the good stuff up top.