The beginning of the game at Aurelion Sol is very simple, until you have not pumped Q to the maximum - you do not have the right to initiate a fight, or get on the provocation to fight. You simply do not have enough time to burn out the enemy with Q.

I - Phase One
Therefore, your phase is like this - you must stack as much as possible, so that your stacks coincide with the time. For example, 20 minutes of play = 200 stacks should be the minimum. So you don't waste Q at the beginning of the game at all! (Unless it's a lot of low-hp creeps in your E), you only use E to build up your advantage.

II - Phase Two
Try to get a feel for this character, you need to understand his limits like any other character but with this one it is EXTREMELY important. Because knowing that you will have 3% xp left after the fight, but you will 100% kill the enemy is important on Aurelion Sol, because that is his fate. I'd like to point out that you should focus on ADC, and try to avoid stuns, of which there are many. Stun is your death. So the second phase is to prioritize killing adk, initiating battles with big ulta near objects.

III - Third phase
It's almost leut, it's time for you to start thinking about making plans for leut. More specifically, do you want to keep stacking, or do you want to finish the game before leut?

IV - Phase Four
As strange as it may sound, this phase is leit, and you are weak in it. A hero with so many stacks on a passive skill is weaker in leut. Because many enemies will realize your tactics, one stun will destroy you and send you to minute respawn.

You can be 30\0\10, but you'll still be weaker in the Leut phase.

V - Bottom line
Aurelion Sol is a strong hero that requires an understanding of his limits. You need to adapt to the matchup and have a good frontline, without it you will be doomed to die. But unfortunately, 90% of the time you can't tank solo, or even duo even if you have a good score. This is at least a mid-game character.