Basically you charm something that's DC-EM then fight things that are T (or all the way up to IT depending on your pet). You have to learn how to participate in battles while keeping hate on your pet. Keep target lock off and if you pull hate, turn around a bit for your pet to get hate again. Sometimes pet choices aren't overly good vs a certain type of mob and you'll have to swap mid-battle. In those cases it's usually better to not melee during the first pet or else it'll be really hard for your second pet to get hate. Just let your first pet get the mob down to about 2/3 of its HP and then drop it, charm another, and go to work meleeing with it. Leave the pet when the mob's about to die and finish it off with a weaponskill if at all possible. Repeat.
Be careful where you leave a mob so it doesn't despawn. If the pet aggros, sneak or invis as soon as you finish the mob so it doesn't aggro you, though if it does you can just charm it again and use leave again. Really after you've been doing it a few levels, all of this becomes second nature. If you're having trouble figuring out where to go, this is a really helpful link.
http://wiki.ffxiclopedia.org/Beastmaster_Post_Update_Viable_Hunting_Grounds
Also, you can just go somewhere like Somepage and find mobs that'll con dc-em to you where there will be T mobs around to kill, though almost all possible camps are listed above where it's realistic to camp without pets despawning.
Edit: And for the love of Pete,
NEVER XP WHILE ANON. There is nothing more frustrating than treking to a really good and isolated camp to find a jackass anon bst there xping. The best thing to do is not only to not be anon, but also to have your camp and your pet and mobs listed in your seacom. An example would look like:
(West) (Nashmau) (Entrance)
(Pet) (Sapling) vs (Enemy) (Bird)
Try to auto-translate as much as you can so you don't confuse JP bsts. If there are multiple camps in a zone, either put your pos or otherwise word out where it is like I did above.
