My TH level is 8 now. I want to get 3 stars, but it is difficult. What is your recommended strategy to succeed in 3 stars attacks?

In town hall level 8, I recommend air attack using dragons and balloons together with the lightning spell.
If you have already upgraded your army camps to the maximum level allowed in town hall 8, then your maximum troop capacity is already for 200 troops.
The maximum army camp for town hall 8 is level 6, each containing 50 troops for a total of 200 troops for all four army camps.
This means that you can have 10 dragons to bring to war since one dragon occupies 20 housing space from your army camp regardless of its level.
The balloons that you will use should be the one you requested from your clan mates as your reinforcement troops.
Ask for the balloon’s maximum level which is level 6 from your clan mates.
You can easily identify a maximum level balloon because it is black in color.
Although balloons move slower, they can be useful in this kind of attack because they target the defensive buildings first.
You can have up to 5 balloons in your clan castle provided that you have upgraded it to the maximum level allowed in town hall 8 which is level 4.
A level 4 clan castle can house 25 troops.
A single balloon occupies 5 housing space.
Also prepare three lightning spells and one poison spell from your dark spell factory.
Plan where you should deploy your dragons to ensure a three star win.
Observe where the air defenses are located.
You should deploy your dragons from the side where you can reach two air defenses the quickest.
Also take note of the air sweeper and its placement in the enemy’s war base.
Always keep in mind to never deploy your dragons on the side facing the air sweeper or they will just blow your troops away and you will lose your chance of winning three bright stars on clan wars.
When you have determined the side from which you will start attacking, kill one air defense first before deploying.
Use the three lightning spell to destroy the air defense which is the farthest from the area from which you will attack.
Make sure that you drop them on the center of the air defense or you will not totally destroy it.
Deploy your dragons evenly on the side where you want them to start attacking.
When the remaining two air defenses start to attack your dragons, drop your balloons behind the dragons.
The balloons will attack the defensive buildings first including the air defenses while they are also busy attacking your dragons.
Use the poison spell to kill the enemy’s reinforcement troops by dropping the spell directly to the troops.
The poison spell will release a poisonous cloud that will make enemy troops slower and will take away their health killing them in the process.
You can drop the barbarian king on the side where you drop your dragons or if there are buildings that are placed very far, then you can drop the king there to save time and destroy the village completely.