What to upgrade first is a problem of every clasher so today I am going to guide you.
The laboratory is key to getting better. Without upgrade laboratory, you can't get better troops in CoC. As a result, you will fail to get 3 stars in war. So your priority should be the laboratory. By upgrading laboratory at TH9 you can upgrade golem and valks to level 4 which will make you a lot better.
Archer queen is the most important factor for winning attack so you should upgrade your AQ to level 5 as soon as possible so you can use her ability.
You should upgrade your army camps as soon as possible so that you can have more army. Without upgrading army camps you can't 3-star fellow TH9s.
Upgrading clan castle will increase your clan castle space. More clan castle space means you can get golem or lava hound in your CC. This will give you a great advantage in battle. Without castle troops, it is always difficult to attack bases.
Xbows are good for defense you should build xbows asap and upgrade them to level 3 so that you can defend your base against attackers
After xbows you should focus on air defense because nowadays air attacks are common so upgrading air defenses will protect your base from air attacks.
Many clashers focus on motors when they upgrade their TH, upgrading mortars will give you nothing. Mortars just do little damage to troops it is better to upgrade archer towers than upgrading mortars.
Wizard towers are very important defense. They can save you from giant attacks. Wizard towers can kill a lot of giants if healing spell is not used.
Teslas are one of most important defense. They can wipe out troops very quickly so you should upgrade teslas after wizard towers.
Now it's time to upgrade mortars. Mortars are good for killing Barch or goblins.
Cannons are good for killing ground troops. They will help you to survive against golem attacks.
After upgrading all of your defense you should upgrade air sweepers. Air sweepers can help you to defend against LavaLoon attacks.
Walls can slow down ground troops so you should at least upgrade your walls to Level 9.
So this was a short guide for all of you. I will write upgrade priority for TH10 and TH11 soon so stay tuned.