Just off the top of my head here are some tips (After finishing i realized how long this is XD)
As a diamond Taliyah main, my advice would be to think of her as an pseudo adc that can basic attack while moving and the basic attacks slow. There exists this sweet zone you want to be in when fighting some one else that is not close enough for them to hit you but close enough where you can hit them while constantly moving and lining up your q, this become a lot easier to do once you have rylies. You want to be close enough where they can escape your q but far enough that they cant hit you. It a lot of moving around and takes a lot of practice. As for her w you simply want to use it in only two instances, when the enemy is getting away (how you secure kills for you and your teammates) and when the enemy is getting to close to you or your teammates. for her w you only want to use it to help line up your w with the slow, place on them so when they dash away they will take damage, place it as a shield against dashing champions to zone them/ discourage them from dashing in, place it behind you when running away from an enemy to create a moderately lasting slow zone. Her ult (once you get comfortable with it) is amazing for roaming, you can also use it to split up the enemy team by separating their back line from their front line when they are moving about and you see a gap, another way of securing kills with her is by chasing with your ult(basically using it like a tf ult) also something new that i just figured out a few games ago is that if the enemy is really close to you, you can fire your ult at them and if you hit them at the right angle you can knock them away in the direction you want them to go, this is made easier around corners and other walls.
I also have two main builds with her, tanky and squishy. I tend to find more success when i build her tanky though and only go squishy if my team has amazing peel for me.
tanky - roa lucid rylies torment hoursglass/warmogs/frozen heart void staff
Squishy - morellos sorc rylies torment ludens void staff
Oh and i bring 10% scaling cool down runes on her, with the rest just bieng focused on defence then pen then ability power
