Leveling up is easy to do, so the focus should be on the main story quests because these unlock new areas and the content in them. Blue quests unlock features like flying, dyes, classes, beast tribes, dungeons, trials and raids.

To level up secondary classes, you can do the dungeon closest to your level (except level 50, 60, 70 or 80 dungeons, these were once max level dungeons so they don't give much experience). There are many other ways to level including hunting log, guildhests, fates, leves, deep dungeons, beast tribes, roulettes, hunt bills and sidequests.

When you reach the first level 50, 60, 70 or 80 quests you are at the end of that expansion and start the patch story quests and side content released in that expansion. So if you have done the level 50 main story quest you can now do all the dungeons, trials and raids that were released in 2013-2015 which appear as blue quests.

Glamour and gear comes from a lot of places and that includes crafted gear on market board and vendors, tomestone gear, dungeons, raids, alliance raids, quests and other places. Most raids have a story version that drops gear and a challenging version which lets you dye the gear. It might seem daunting that there is gear locked behind challenging raids, but when it gets old and we have a higher level than the raid, the raids are a lot easier.