Pick a simple goal or idea for your AddOn. It's often a good idea to just make an AddOn that only opens a window or prints a message to get started, especially when everything is new for you. After that works the way it should, and you have learned everything necessary to make an AddOn work at all, you can move on to adding one piece at a time toward your goals. Writting software in general is often a never ending process because you can always think of something new to add or improve.
Research instances appropriate for your level online. Running instanced content is the single most important thing you can do, at least up through level 85. Instead of focusing on questing, focus on dungeons. A quick search for “WoW dungeons by level” or similar will help you find the right instances for your level. Keep in mind too that many instances are faction specific, so make sure to check Horde or Alliance specific lists!
This Addon solves that issue where you have 5 Paladins in your Raid and no one can decide who is Buffing what. It has a little UI that represents Different Classes in your Party or Raid. You can change what buffs you want to give out then just mash the Class Button for each Class type until they all Turn Green. If anyone is missing a buff you are assigned the Class
At level 80, I skipped Cataclysm and went straight to Pandaria. Even as my warrior leveled up, and that heirloom axe increased in iLvl along with me, Dugi still ranked that iLvl 87 sword higher. I kept picking up new 2h weapons, and Dugi kept rejecting them in favor of that Wrath sword. That's when I noticed that all of these Pandaria weapon drops, even weapons 20 iLvls higher than the Wrath sword, had secondaries under 20. So even though Dugi Gear Advisor is showing that a new weapon would provide a DPS increase, it still prompts me to re-equip that Wrath sword every time I equip a new weapon. Meanwhile, I've kept the heirloom axe in my bags, assuming that at some point its stats would once again beat whatever I had equipped, but nope, it doesn't, according to Dugi.
As the first major content release of Battle for Azeroth, patch 8.1: Tides of Vengeance is adding a number of new ways to gear up, as well as increasing the item level of rewards from existing activities. Tides of Vengeance goes live on December 11th and will add most of the new content, but Mythic+ and PvP Season 2 will not start until the new raid, Battle of Dazar'alor, releases in January, at which time the item level thresholds will increase to the new Titanforge cap of 425.
Drustvar is far and away the hardest Alliance zone, which is exactly why you want to do it first. If you have legendary items, they’ll still be usable, and if you don’t, this zone will still be easier early on than it will be later. Drustvar is also extremely fast and will let you jump out ahead of your competition in other zones, which means fewer players around to take your quest objectives.