I thought I might share some of my own experiences, or coming experiences (seeing that I'm still young), with unique songwriting. It will also feature some methods to arrange the song. Note: it may be a bit long, so take it one step at a time.
Most of my knowledge in unique song writing comes from studying the bands who do it. Most of you who read this article, may not be familiar with these bands. Most of them can be labelled progressive, but that is not a must. Examples of these bands are:
Symphony X
Check them out if you haven't already. Progressive music is probably the only musical genre where you in advance knows least what to expect. Some things comes and goes, like long songs and high technical mastery of the band members' respective instruments, but there are no rules. What [i]you[/i] gotta do is to listen to the song, maybe even learn them. You will learn a lot about songwriting by learning and listening to songs. Here are some examples of methods to use while writing unique songs:
Dynamics
What are dynamics? Think about the conductor in an orchestra. He controls the players and decide wether to play softly or loudly, although they are still playing the same notes in the speed no matter how hard he tries to make them speed up. So a piece of music can be played in many ways considering the use of quiet/loud dynamics. In an acoustic passage one might play soft and slowly, but the acoustic guitar can be played both loudly and fast. Speed is also a valuable dynamic. Listen to Opeth's "Advent" at 3:19. That acoustic guitar is quite fast (not shred though), and serves another purpose than the outro (which is quite slow). It keeps the intensity up, and when the electric guitar comes back, you don't feel relaxed. So just because you're a death metal doesn't mean you can have soft acoustic noodling or ballads. Try to stretch out. I always thought Opeth was one of the bands with the most extreme dynamics, and it gives them so much more oppurtunities when writing a song, instead of some grindcore band who's determined to play fast and hard all the time.
Think Outside The Box
When writing unique songs, you have to think wide. You have to do stuff you normally wouldn't do (unless you're a jazz/pop/metal/rock/reggae/ska-guitarist or something like that). Try to look back at your previous songs and notice what you tend to do a lot. Some of it might be your "style" or "sound", but seen by others that can be a sign of little variation. Do you always write in 4/4? Are all your chord progressions standard? Are all your songs circling around a specific number of minutes? Try varying!
The most standard riff you probably could create would be something like this:
1 2 3 4
|---------------------------------|
|---------------------------------|
|-9--7--5--5----------------------|
|-9--7--5--5----------------------|
|-7--5--3--3----------------------|
|---------------------------------|
It has 4 notes in a 4/4 beat, it uses only power chords and the chord progression is the simplest you can do with three chords. So what can you do to make it more interesting? Take a look at this:
1 2 3 4
|-7-7--5---------0----------------|
|-8-8--5---------3----------------|
|-9-9--7----5----2-2--------------|
|-9-9--7----5----2-2--------------|
|-7-7--5----3----0-0--------------|
|---------------------------------|
You still count to four, but the riff is definitively more advanced. Why? First, you use something than power chords, but you also don't just move the same chord around in different keys. Plus, at some counts you have 1 chords, but at some there's 2. That means that the last count doesn't replicate the last one by just moving it to another key. Let us spice it up with some more techniques, shall we?
1 2 3 4 5
|-7-7--5-----------0----4-2-------|
|-7h8--5-----------3----4-2-------|
|-9-9--7----5---5--2-2--4-3-------|
|-9-9--7----5-5----2-2--6-4-------|
|-7-7--5----3------0-0--6-4-------|
|-----------------------4-2-------|
The riff has moved to 5/4 (meaning 5 counts instead of four... I think). That's like jazz, you know? At the first count you also mix hammer-ons with chords, something I could never come up with myself. I saw it in an Opeth tab, because I were studying the song. Get it? Count three also use arpeggios, which is used very rarely with distortion (so you're either gonna have to palm mute the notes or let the finger of the last one go when you play the next). Count 5 doesn't even stay in the same key. This is just basic of course. That riff probably doesn't sound good, but feel free to steal it (I just made it up in the tab). Now take a look at this:
Head 1 Tail 1 Head 1 Tail 3
|-----------|-----------|-----------|-----------|
|-----------|-----------|-----------|-----------|
|-----------|-----------|-----------|-----------|
|-----------|-----------|-----------|-----------|
|-----------|-----------|-----------|-----------|
|-----------|-----------|-----------|-----------|
Head 1 Tail 1 Head 1 Tail 3
|-----------|-----------|-----------|-----------|
|-----------|-----------|-----------|-----------|
|-----------|-----------|-----------|-----------|
|-----------|-----------|-----------|-----------|
|-----------|-----------|-----------|-----------|
|-----------|-----------|-----------|-----------|
What you get here is a long riff. A long riff will serve you better than a short riff (but take notice that long riffs may be extensions of several mini-riffs). What you do here is to use "Head 1" as the start of the riff, play a ending to that ("Tail 1"), repeat "Head 1" and end with a second ending, "Tail 2". Then you can move it to 8 beats, giving a last ending ("Tail 3").
Example:
Head 1 Tail 1 Head 1 Tail 2
|-----------|-----------|-----------|-----------|
|-----------|-----------|-----------|-----------|
|-----------|-----------|-----------|-------4-5-|
|-5-5-5-5-5-|-----------|-5-5-5-5-5-|-----2-----|
|-5-5-5-5-5-|-4-5-6-----|-5-5-5-5-5-|---2-------|
|-3-3-3-3-3-|-------5-4-|-3-3-3-3-3-|-1---------|
Head 1 Tail 1 Head 1 Tail 3
|-----------|-----------|-----------|-----------|
|-----------|-----------|-----------|-----------|
|-----------|-----------|-----------|-5-4-------|
|-5-5-5-5-5-|-----------|-5-5-5-5-5-|-----2-----|
|-5-5-5-5-5-|-4-5-6-----|-5-5-5-5-5-|-------2---|
|-----------|-------5-4-|-----------|---------1-|
Also, did you know that Metallica's "Enter Sandman" riff was originally written like this:
|-------------------------------|
|-------------------------------|
|-------------------------------|
|-------------------------------|
|-----7--------5---4---4-5-4-2--|
|-0-0---6-5--0-3-0-2-0-2-3-2-0--|
Don't see any difference? This is how it's played now:
|-----------------------------------------------------------|
|-----------------------------------------------------------|
|-----------------------------------------------------------|
|-----------------------------------------------------------|
|-----7------------7------------7----------5---4---4-5-4-2--|
|-0-0---6-5--0-0-0---6-5--0-0-0---6-5-0--0-3-0-2-0-2-3-2-0--|
I think you'll figure this one out yourself.
The Arrangment
Now that you know how to write "unusual", let's see how we can use that in a larger setting. Again, I'll use Opeth as an example. If you don't like that the band, that's fine, but don't give me 1 star just because of that. If you look at Opeth's first album "Orchid", you'll definitively see that the songwriting and arrangments are pretty raw. The songs have LOTS of riffs. Is that a good thing? Not necessarily. It's better to have 5 super-good riffs than 20 mediocre, right? I'm not saying that anything on "Orchid" is mediocre, I'm just giving an example. Again, try to merge some of your own 20-something riffs to 5-10 longer and better riffs. It can't hurt, can it? If you look at "Master's Apprentices" from their newer album "Deliverance", you can see that the songwriting of the band has increased. You might not agree that the song is better, but it shows a more mature aspect of writing (judging completely on structure instead of sound). The songs on "Orchid" constantly jump back and forth between acoustic and electric, while "Master's Apprentices" has only one acoustic passage. It's a long one in the middle, but the song doesn't feel long.
Also look at the "The Leper Affinity". Only one acoustic passage, but more use of dynamics in the electric guitar. Listen to the song at about 3:30-4:00. That section use extreme dynamics. Then it glides gently into a softer (but still electric) riff at 4:00, before at last giving in to the acoustic guitar. A good example of using the same instrument in different dynamics. To make it all flow really good, write it all on an acoustic guitar (or electric guitar on clean channel). Make sure you write it so sounds good on acoustic guitar. That means that long, ringing power chords won't sound good. It gives a stricter demand, but in ten years you're gonna be glad you pushed yourself. Have a high demand for riffs.
Did you notice that some songs can be seen as "cheating". It's like "make two riffs and then you'll have a song". That's cool, I know cool songs with only 1 riff, but that isn't very unique is it? I myself like how the second half of a long song can be completely different than the beginning of the song, instead of hearing the first verse with different lyrics and then the same chorus again. Try to put something special in your song that's gonna make people remember it. Like the opera in "Bohemian Rhapsody" or the 11 guitar solos in "Hangar 18". You might hate opera and you might hate guitar solos, but you can't argue that those songs have something few other rock songs has.
Stay tuned, and remember to study the bands!
/ my profile 
