Off the top of my head.
1: the game is not WoW, its a mainline final fantasy so its not "gogogogogogogo" to rush to max level.
2: dont pay to level boost since you still need to do the story anyway, theres also a paid story skip but it would just make everything confusing
3:You start in one of 3 cities based on class and the common agreement is Uldah has the best origin story, Limsa Lominsa is the easiest, but its also an island nation so you are cut off from the larger world till like level 20ish or higher and gridania is 'fine' but the story is the weakest and the area while pretty is kind of boring quest wise in comparison.
4:This is a final fantasy using the job system. Your character is your account. You start on one class but by level 10 you can go to any other class guild and do the starter quest, equip the weapon they give you and be a lvl.1 of that class. You can do everything and level every job on one character which most people do so if you dont like the class each city has alternatives.
5:You will start as a 'greenleaf' which means you have a green leaf by your name to let others know you are new. This isn't a mark of shame and in this game a wipe in a dungeon isnt an instant abandon ship scenario like most wipes in a WoW dungeon finder experience. There are times where you will need to know a fight e.g: boss casts doom and if you dont run to a glowing mark on the floor before the countdown you die instantly and its totally fine to ask what the strat is and 99 times out of 100 people will be fully willing to explain.
6: crafters and gatherers are their own job with gear, quests and stories. If you want gil early your best bet is just seeing what low level material thats used at high level like silver is the most valuable and level a gatherer by farming some of that and selling it
7
ont feel like you need to rush. There is a 1-50 experience and story but at 50 you dont just jump into heavensward like you do outland in WoW. There was a 2.1-HW set of patches with primal/summon fights, a storyline, raids, hard mode dungeons which are revisits to dungeons but the layouts changed and new enemies/bosses show up that you go through first. Which also means if you stick to one job you will probably get a buttload of xp we didnt have when HW came out.
8:Gear is a much smaller number increase as you go on so dont be afraid to spend time in stuff like triple triad, chocobo breeding/racing, the gold saucer, lords of verminion, hunting logs, anything that takes your fancy. We are about to get the last major patch till the expansion in early summer 2019 so its not like people are going to keep getting ahead of you right now.
9:If you bought the collection don't be afraid to try new jobs. They don't all start at lvl1. Ninja and in the next patch Blue Mage start at lvl.1 like the launch classes that turn into jobs at lvl.30 and later jobs dont need classes. You just run into the questlines that get you the job crystal and weapon to job change. For example Heavensward gets the Dark Knight tank, Astrologian healer and Machinist dps which start at lvl.30 and if you have Stormblood Red Mage and Samurai are both dps that start at lvl.50. I found say dungeon tanking and healing is easier than in WoW but unlike WoW a healer not also dpsing is considered pretty lazy and holding the party back as a big faux pas. The usual recommendation is pick one tank be it Warrior, Paladin or Dark Knight, one healer be it White Mage, Scholar or Astrologian and any dps you like so you always have something to swap to.
10
ont bother with housing till high level, its basically a moneypit, dont buy any gear from the market board/ah before max level to save gil and always check your daily/weekly challenge log for very simple things that will give you free easy money.
11:If you are a fan of the other mainline games try not to skip cutscenes, there are moments where the story puts games like 8-13 to shame and the music in particular is worth sitting through
I would recommend starting in limsa lominsa as arcanist. Get to lvl.10 and unlock Rogue which becomes Ninja but also gets you Arcanist right away which is the only class that becomes two jobs, the ranged dps Summoner and Pet using healer Scholar. You can also go right to a place at lvl.10-15 called the hall of the novice that teaches the basics of the three trinity roles, gets a set of gear for each and a 30% bonus xp ring.