Whats the best way to get the best gear? Running dungeons all the time (because i dont know if the gear u get in them gets better every time u run it) ? Buying at the AH? Id appreciate your advise,
Thanks!
The exact details will depend on your class/spec.
AH is a good start, BoEs are BiS in most slots -
this wonderful thread will give you a good idea of what you're looking for. Leather wearers will definitely want to hit up the Arathi Basin vendors for belt/boots (1 mark of honor each), and the ring from the WSG vendor is solid for casters.
Dungeon gear is all decent, it's about the same as heirlooms but with more options for secondary stats. It's just scaled to your level, no changes from running them more often. You can usually get a couple extra stat points from BoEs, but dungeons are a good starting point if your AH is dry or overpriced. There are a couple nice rings in them too. The in-game dungeon journal is the best way to look at loot in them, wowhead's kind of cluttered now that everything scales.
Mindtap Talisman and Vigilance Charm from Dire Maul are best all-around trinkets for most specs. You can try hitting up the in-game communities to look for people to run with, going with other 39s speeds up farming a lot.
Engineering is useful for everyone. It's especially important for casters since Green Lens and Spellpower Goggles are generally the best helm options.
Here's a quick guide on leveling that. If you don't have the gold to buy mats, you can farm everything in an hour or two on a class trial druid.