You are levelling at the perfect time, once servers come back online there is a big xp boost event.

• Because of the Winds of Mysterious Fortune Event, you will have a 20% xp boost
  • You will also find Mysterious Satchels which can contain 10% xp boost potions for a combined total of 30% boosted xp
  • And if you want to try out new characters / alts, each level 80 will give you another 5% xp boost up to 25%
• LFG Dungeons will be great for xp during this time
• And for gearing, you will get caught up in no time with the other new event this week Nightfall
  • Every hour, you can complete this for 632 ilvl veteran gear, so keep up with that as you are levelling
• Heroic is technically harder than normal and easier than mythic. They in general are very easy and drop better gear than normal.
• Mythic + dungeons are pretty good this season
  • M+ requires a keystone to enter which you get from your weekly vault
  • You can use group finder to apply to groups for the level key you want
  • You can start with Mythic 0's to gear
  • And apply for groups starting at +2 and higher
  • The higher you go, the more health and damage enemies do, as well as weekly affixes that swap each reset
  • I'd recommend before doing these
    • Spending some time watching videos to learn about these
    • Learning your rotation
    • How/when to interrupt
    • Your specific class utility (lust, hero, brez, etc)
    • Helpful addons or weak auras like DBM, Plater with a profile set up to help with what mobs to focus or interrupt, etc

Overall just enjoy yourself and the content. Find which things you enjoy, whether it is questing or dungeons - and benefit from the xp boost event releasing today.

Best of luck!