It definitely takes time and you will fail a lot untill you internalize this stuff. I suggest you to lower your standards a bit so you have more sets to practice with, most if not all of them will go nowhere anyway. Also, don't send a single line because you just saw Alex or anyone using you'll probably come across as incognurent and it'll blow out. Understand the principal behind the line and then decide to use it or come with your own

Don't just read his interactions. Analyze them and extract patterns. Then practice what you learned with lots of girls