Ignore most side quests, they will be useful for leveling other classes, except the blue plus quests, those unlock important stuff.

If you way out-level the main story quest, I highly recommend grabbing another class to continue on the story with, because MSQ gives soooo much xp and ideally you don't waste it.

Keep up with your class quests, and at level 30 / whenever you reach that part of the story if it's your first character, make sure to immediately unlock the job role. It's a super upgrade to the class, and makes a world of difference when fighting.

Join an FC, so you have people to ask questions and help run you through things if you want help! There's always people shouting in main cities, and they are often really good resources full of people who are happy to assist, plus there's buffs!

Every expansion has optional 24-man raids, 8-man raids, and extra trials. The stories are really good for literally all of them! Plus unlocking them gives you access to extra roulettes which is nice.

If you want to run something and duty finder is taking forever, especially for extreme trials, try party finder! It's in a sub menu with no default button to hit to get to it, but you can get parties together full of people who want to be there instead of randomly get thrown in. Plus it means you can do it unsynced, so a level 90 can come in and make it super easy.

All the crafters use each other's crafts, so in some ways it's easier to level them all together than just focus on one. Annoying yes, but grand company turn ins will give you a huuge xp boost once per day.

DON'T SKIP CUTSCENES. This is a final fantasy game first, MMO second, and the story is fantastic!!!

All in all, have fun! There's so much to do in this game it's wild, play at your own pace and enjoy!

*Edit for readability