I know what both mean and are used for, but when I look at my reference materials, the former is often used to express the same thing as the latter. Are details to this that I'm not getting?
I will assume by 「ていく」 you do not mean "Do something and leave".
When you are 「ている」, you are doing it now. No reference to the future.
When you will 「ていく」, you will do it from now, from this point on.
「ていく」implies continued effort, where as 「ている」 is only about what you are doing now.
「ていく」doesn't necessarily imply that you weren't doing it before. It depends on the context. (i.e.「これからも引き続き工場の安全を確保するために全力を尽くして行きたいと思っております。」= "We will continue to work hard to maintain safety at our factories.")