I know a bit of theory, and I am fairly decent at guitar. but everytime i try to write a post-hardcore song, similar to the Chiodos, i just can't find a good progression to use for the rhythm. any tips would help please.
Use any of the following chords A B C D E or F and don't be afraid to throw the odd sharp or flat chord in
Just pick a scale and mess around in it. If something doesn't sound quite right try something else, but writing stuff with power chords is pretty easy.
Quote by HEXAGRAM66
Sorry forgot G! that last post could have been really unhelpful without G!!

Even with the G it was really unhelpful. I suggest both of you to take a look at the sticky and lessons around the site. I'm over 9000% sure you will find your answer in one of those.
Imply a chord progression like a good composer and don't assume powerchords are real chords, due to the parallel fifths in them they only sound like louder, beefier single notes. Check the first note of the melody of every bar and make a chord with it. So if I had a melody like this:
A, B, C#|D, E, F#|G# A, B| C#

I would make chords with the melody by playing these powerchords for each bar


Although this looks like a V-vi-V-I progression, it's actually a standard I-IV-V-I progression because the powerchords form chords with the melody.
E and an A make an A chord. F# and a D make a D chord. E and a G# make an E major chord. A and a C# make an A major chord.

Just a little idea for you.
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[U]      //| \      |       |      [/U]
[U]     | \|_ |     |     .-|      [/U]
      *-|-*    (_)     `-’