Can someone please explain to me how to keep a strong shot low on advanced shooting? Let’s say, I am going left to right and want to shoot it low in the left corner with some power. What do you press/hold how long and where do you point the stick at?
Currently, all my shoots balloon up, even short taps.
You basically have to aim towards your own goal.
I know that sounds ridiculous, but I'll try to explain it:
So as you said, let's say you're shooting from left to right:

aims for the top right corner

aims for the top left corner

aims for the bottom left corner

aims for the bottom right corner
Basically, power doesn't dictate what corner you're aiming for. At all. So, if you have an open goal, and you aim

you have every chance to put it over because even though you've tapped the button you're still aiming for that top corner.
To make your life much easier you MUST learn to press shoot before you aim. Let's say you want your striker to hit a first time shot into the bottom corner, if you press

first, then shoot, your player is just going to do the first command you pressed, which is to turn around and face away from goal; which is INCREDIBLY frustrating! You may pick this part up really easily, but that was the main thing I had to get around. Once you've sussed it though you can do things like powerful placed shots into the bottom corner, which cannot even be attempted on Basic. You can also do really cool looking low arched chips because you can aim chip shots specifically for the bottom corner.
In terms of power, you can basically hit it full power with everyone if you want to. You know how when you hit a short pass with full power the ball will rise up if they aren't that great at passing? Well advanced shooting works in the same manner; so if you were to use Chris Smalling to hit a full powered shot into the bottom corner, chances are it'll rise up and aim for the top corner naturally (well, more likely it'll spoon off towards the corner flag, but you get my point).
I'd recommend playing a game on the easiest setting and just get lots and lots of different shots in to sort the muscle memory out.
Hope that helps!