What is a good design pattern to avoid having to use a global variable at the top your main form?

Every time I talk to experienced programmers, they talk about having global variables being a bad practice because of debugging or security exploits. I have a simple List of strings I want to load from a a textfile and access across different methods in my form. Before, I would simply initialize said variable at the top, inside of my form class and use it across methods. I always try to reduce that practice when I can and only initialize those variables when I really need them. Is it a bad practice to do this or do more experienced programmers do this too? Is there a standard design pattern method of doing this so you don't have to use "global variables" at the top of your form?