So you're finally 70. Welcome to the select order of masochistic players who endured the tedious grind (or, if you leveled as Protection, the happy AoE grind) to max level with a class sometimes considered to be a WoW developer's afterthought. The Paladin class, popular as it is, has traditionally had a slow development cycle. That said, one can choose to see it as a blessing (pardon the pun) rather than a curse, in the hopes that developers will build Paladin talents adaptively and from the lessons provided by other classes. Don't hold your breath.
Anyway, so you're Level 70. You're now ready to enter Karazhan. Well, ok, not really. Right about now is when you should be gearing up for Karazhan, The Burning Crusade's entry level and most popular raid instance. With the removal of the attunement process in Patch 2.4, you won't even need to have The Master's Key, but you'll need to have a friend who can open the gate for you. More than a few Holy Paladins will have an easy time getting into a group for Karazhan because let's face it, everybody loves a healer. Then there are the Paladin tanks who'll get that loving invite to visit Deadwind Pass because, again, everybody loves a tank. But you, the vindictive 2-hander-wielding, Judgement-spamming, Crusader Striking champion of truth and justice... well, nobody loves you.