This is where, as a composer, you "live or die" on your own. As a composer you will have to make the "approach" type of decision every time you take on (or even apply for) a film score. What you don't have is the input from the director. Believe it or not, this is not unusual. Though they vehemently protest that they don't think this way, they are 30% to 70% "I'll know it when I hear it," or else they are so married to their temp music they can't get past it. So you will have to know what the proper approach is; you're the one guiding the director.
Now, I want you to understand that I'm not being flippant here.
Go back and reread your post.
my name is Connor i am a film student from England and i am currently working on a creative/experimental project, i am composing a piece of music for David Lynch's Eraserhead. I am seeking advice on how to approach this as i am a first time composer and a self taught guitar player. I'm hoping to capture an industrial, dark feel to the composition, the only instrument i am using is an electric guitar and i am wanting to use sound FX using a microphone and Tascam to incorporate into the piece. your help would be much appreciated.
You have already answered most of your own questions.
I am currently working on a creative/experimental project, i am composing a piece of music for David Lynch's Eraserhead.
The key phrase her is
creative/experimental project. So go ahead, experiment. Be crazy, be stupid, be creative.
I'm hoping to capture an industrial, dark feel to the composition
That's where you start.
i am using is an electric guitar
That's your "noise maker." Remember that it's not just about strings and picking. There's the pick-ups, and tuning, and amplification, and micing techniques, and unusual ways of attacking the strings (thumb thumps, pick scrapes, violin bow, E-Bow, etc. Ever here of "prepared piano?" Apply that concept to the electric guitar!)
Now, with all of this at your disposal, what sounds can you make that are "dark and industrial."
Now, watch the scene for which you are composing. What are the high points and low points? What are the emotions? You've now got some idea of what your sound palette is; apply them to the arc of the scene. Find a theme. Now, go back to my earlier comment - Experiment. Be crazy, be stupid, be creative.
Just for fun:
https://www.youtube.com/watch?v=kc3-C7Lnzh0
https://www.youtube.com/watch?v=ex57oiPSxKc