Clash of Clans Upgrade Order Guide: General Rules
Upgrade Priority #1: Laboratory: Builder #1
At any Town Hall level, your top priority should be to upgrade the Laboratory. Upgrading units via research is the easiest and most effective way to increase your farming and war capabilities. Not only that, but research is often the most time-intensive step of a given Town Hall level. Upgrading the Laboratory early ensures you have enough time to complete your research by the time you move on to the next Town Hall level.
Upgrade Priority #2: New Barracks & New Army Camps: Builder #2
While your first builder can work on the Laboratory, any other free builders should start building any new Barracks or Army Camps that may have unlocked (only a few Town Halls add extra Barracks and Army Camps). This does not refer to upgrading old Army Camps or Barracks, but rather new ones. Adding a new Barracks or Army Camp significantly improves production and capacity respectively, significantly improving your farming abilities.
Upgrade Priority #3: Spell Factory & Army Camp Upgrades
After the Laboratory and new Barracks and Army Camps, the third priority task should be upgrading the Spell Factory and any Army Camps that are not max level. The reason for upgrading these relatively early is that upgrading either of these structures will increase your offensive capabilities, improving your farming and war capabilities.
At high levels (TH9+), upgrading your Army Camps this early is not only not recommended, but not practical given the high cost and long build time. While you will still upgrade the Army Camps before upgrading old towers, you may find it easier to build some of the “priority 4″ structures before upgrading all your camps.
Upgrade Priority #4: New Towers, New Walls, Storage Structures, and Dark Elixir Drills
After maxing out your offensive capabilities, it is time to start upgrading your defensive capabilities. The fastest way to improve your defensive skills is to add on new towers, complete their early upgrades (especially for the Cannon and Archer Tower), add new walls (do not max walls out at this step), and build additional storage structures.
Adding additional storage structures (gold and elixir storage) is actually more beneficial than most players realize. The amount of resources an opponent can steal is capped, so with additional storage structures, it becomes more difficult for the opponent to get access to all of your resources.
In this upgrade tier we will also include the Dark Elixir Drills. I like to upgrade these as a fairly high priority, given that Dark Elixir is a very limited resource and the drills produce quite a bit of it.
Upgrade Priority #5: Old Towers
After going for the easy and fast addition of new towers and walls, you should be ready to set up a good base layout for your new Town Hall. After you do that, you can start upgrading your existing defensive structures to their next levels. Be sure not to upgrade more than one Air Defense tower at a time; doing so will make you very vulnerable to enemy air attacks.
Upgrade Priority #6: Everything Else
At this point, you can upgrade your remaining structures as the resources become available. This includes things like leveling up your Barracks or Dark Barracks to the max level, upgrading resource collectors, and upgrading walls. These are all low-priority tasks that you can do as you get the resources.