Don't throw away your level 1 crappy white weapon.
Don't use the new faction outfit you get early on, it enables PK. But don't throw it away.
Don't drop/sell the purple weapon you're given early on by the NPC (It's your Hongmoon weapon and it's your endgame wep.).
Don't forget to grab professions when you first reach Jadestone Village, you don't have to level them, but the gathering professions would help you gain an extra bits of exp.
Don't use any green weapon upgrade pills to upgrade your weapon, you will regret it, use it very late in the game.
Purple rings and earrings you get from the quest are your Hongmoon accessories, don't throw/sell them away.
Don't forget to do a few of the daily quests (one's with white strips on the blue arrow) which gives you crafting mats and/or heroic stones (black stones with green/red/blue symbols on it)
Don't farm purple dungeons for bopaes/soul shields, use the heroic bopaes from trading the above heroic stones instead, until you get your scorpion bopae later.
Don't waste money on bidding for too much BNS Gold in lower level dungeons, it's not worth it.
Treat Unsealing Charms like it's your last triple cheese meatlover pizza, regardless of how many you have in your pocket.
Don't use your Hongmoon Weapon in Arenas, use the crappy white weapon.
Spamming keys to open up chest is fine, but don't overdo it, trade with others if you can (you can't trade purple weapons though). Only use the HM keys if you know what you're doing.
Don't throw away the Bell.
Don't use XP food when you are at the same level or above the map you're doing quests/grinding.
Repair tools are precious during first few days of a new server, be careful when you repair your weapons.
Don't worry if you picked the 'wrong' faction, you can switch faction later.