Upgrade your buildings and defenses on the right order is extremely important on Clash of Clans and severely affects the gameplay. Making errors could cost you a lot of time and resources and be very frustrating.
On this tutorial I will share my Upgrade Priorities list. There are many different approaches on this game, but on this list I will share an aggressive upgrade order so you can progress on the game fast and don't struggle wasting too much time stuck on a Town Hall level. It's a list that will give you some challenges, but will not make let the game being too slow and frustrating.
2. Storages, Laboratory, Spell Factory
3. Clan Castle, Barracks, Army Camp, Spell Factory
4. If you are TH12: Giga Tesla
5. If you are TH11: Eagle Artillery
6. If you are TH 10: Inferno, X-Bows
7. If you are TH 9: X-Bows
8. Collectors, Mines, Drills
9. Other defenses: below TH11 first Splash Damage defenses, above first Single Target defenses
10. Town Hall
Yes, Heroes. Why? It takes over 280 days to reach level 60 King or Queen, so the sooner you start, the better. If possible, upgrade them non-stop. If you are skipping wars to upgrade your Heroes, upgrade all of them at the same time.
Heroes are the most important upgrade on the game. It's more important than any defense or regular troop. If you have maxed Heroes you own the game and can attack any village regardless of defenses or base layout. So don't waste any time and go for it!
2. Storages, Laboratory
Storages are a very important upgrade for two reasons: bigger storages are necessary to certain upgrades and it's important to have more space to hold resources when all builders are busy.
Laboratory is a great upgrade so you can upgrade your favorite troop as soon as possible. However, the most important thing is to keep your Laboratory always busy, never let it stop, always research something. Maxing out all troops and spells on the Laboratory is quite hard and even maxed TH 12 players struggle to finish everything, so keep it working all the time.
3. Clan Castle, Barracks, Army Camp, Spell Factory
Now it's time to make room to more troops on your camps and unlock new troops and spells. Barracks upgrades really depends on your level and which troop you will unlock, but overall it's a great idea to unlock new troops right away so you can start upgrading them on the Laboratory. Unlocking new troops also helps to make the game fresh, so go for it.
However, it's not really necessary to upgrade all your Barracks. To unlock a new troop you only need a single Barrack upgraded. The other ones will only make the training of this troop faster. Since the troop level will be too low to actually use on battles when unlocked, you can wait to upgrade all Barracks until the troop level is high enough to use on battles.
The upgrade order of the defenses depends on your Town Hall. I recommend upgrading the new defense right away (TH12: Giga Tesla, TH11: Eagle Artillery, TH10: Inferno Towers).
However this is an aggressive strategy to push and level up faster. These defenses affect heavily the weight of your base on Clan Wars, specially maxing out the Giga Tesla.
Worrying about the War weight is a safe strategy, but if you follow the priorities correctly and only upgrade your Town Hall once you finished all defenses, I don't really see a problem in upgrading these defenses right away. I don't really recommend TH9.5 bases anymore, specially now that Clan War Leagues were introduced and the matchmaking is solely based on the League your Clan is.
The other defenses also depends on your Town Hall level: on lower levels (TH10 and below), splash damage defenses have higher priority. Once you reach higher Town Hall levels, single target defenses start to be more important.
5. Town Hall
At last, the Town Hall! This should always be the last upgrade of your Multiplayer Base mainly because the loot is based on your Town Hall level.
There is a loot penalty for attacking Town Halls below your level, so you only should upgrade when you are ready to farm against the new Town Hall level. The loot math is based on your Town Hall level as well.
You can rush all the way to TH 7 to get the 4th Barrack and Army Camp (it’s a new game with 4 Barracks). But then take some time and upgrade troops and defenses, make all upgrades available and only then level up your TH, otherwise it will get too difficult to raid for resources since you are not strong enough to battle players with the same TH as yours.
Don’t rush your TH to level 10, 11 and 12 without upgrading all defenses under any circumstances! This will affect your loot since you will not have strong troops to attack the same Town Hall level and you will not have a strong defense to hold resources against them.
Remember, the game wants you to battle against opponents with same Town Hall level as you! This is done by the matchmaking and by reducing the loot available when you battle against a lower Town Hall level. You should only upgrade your Town Hall when you think you are ready to attack and defend against the new level.
There is no consensus if you should finish your walls before upgrading your Town Hall or not, but I strongly recommend upgrading your Town Hall even if you didn't finish the walls. Once you finish the defenses, just go for it.
Maxing out all walls takes a lot of time and can be frustrating as it will hold your progress on the rest of the village. Another reason: walls are not really that important on higher levels and doesn't affect the gameplay that much, so don't worry too much about walls.