I'm going to do this in chunks, because I've been writing it out and it's getting long. This won't be so much of a leveling guide as a Marksman guide. Leveling is pretty general - go to zones where you can get quests and don't die immediately walking out of town, and kill mobs and do quests. Leveling as a Marksman in particular, on the other hand, means knowing what you want for talents, what your skills are useful for, and what kind of gear you should be using. So then:
A lot of people level as Beast Mastery. It's easy - send in the pet, turn on Auto Shot, let the pet do all the work. Marksman doesn't have to be hard, though. Leveling as a Marksman hunter can help you develop some skills useful later in the game, since you can't always count on your pet or your tank to hold every mob in a pull (and sometimes you don't want them to, either). Kiting and chain trapping will always be more in the realm of Survival, just because they have talents built towards minimizing snares on the hunter and maximizing traps. These skills can, however, be learned and developed as a leveling Marksman hunter.
General Talent Notes
I run with two Marksman builds; one is geared towards a generalist playstyle - soloing, casual PVP, instances - and the other is focused on raid DPS output. The former is the one you'll want to look at for a leveling or soloing build - 7/53/11. You'd probably want to do Marksmanship talents first until around when you've got Improved Barrage filled out, then pick up probably the Survival talents to get Scatter Shot. (Or, if you're impatient, toss the 7 points into Beast Mastery for a faster pet revive.)
Soloing Spec (7/53/11)
Raiding Spec (2/62/7)
Survival talents: Scatter Shot is fantastic in solo and small group play - it's short term crowd control, which you can use either to extend locking down a mob until your trap cooldown is back up, or use it to get a mob off your healer or a clothie until you can either get it trapped, or your tank picks it back up, or you can hit it with enough damage to pull it off to kite it. It's also another spell interrupt, and lasts long enough for most of a fast pet revive. Improved Tracking (5% more damage against most mobs), Hawkeye (another 6 yards of range), and Survival Instincts (4% less damage taken and 4% more crit for Arcane and Steady Shot) are good ways to get there.
Beast Mastery talents: Improved Revive Pet is awesome. If you're mostly soloing and your pet doesn't hold aggro well (and after a while, it probably won't, if your gear keeps up), use Endurance Training (10% more pet health, 5% more health for you) to get it, instead of Improved Aspect of the Hawk (10% chance to proc a haste boost) - you'll probably be kiting too much while soloing to really take advantage of the haste proc.
Next up: A more detailed look at Marksman talents.