How do I learn to think several moves ahead like senior lawyers?

You can handle the task in front of you, and that is where everyone starts. Seeing three moves ahead feels like a gift the partners were born with, but it is not. It is pattern built from having watched hundreds of cases play out. They are not smarter than you. They have simply seen more, and remembered it. You close that gap by studying how cases end, not just how they begin. Every time a matter resolves, look back and trace the moves that got it there. Ask a partner why they chose a certain step and what they were setting up. You are borrowing their experience to grow your own faster. Start a simple habit: on your current work, force yourself to write down what you think the other side will do next and what you would do in response. Check later whether you were right. Doing that over and over is how foresight gets built. It is a trained skill, and you are training it.