I know chords in general, bar chords, power chords, the blues scale, the pentatonic scale, and I recently learned some new scales called Aeolian, Lydian and Harmonic Minor. The problem is that I can't break out of the scales, and create repetitive and forced... Also when I play chords, be it power chords or anything else, I keep playing only what I know or have heard of others and it's hard to forge my own style out of it...
What inspires me the most is Children of Bodom, In Flames, NORTHER and Metallica and Lazarus A.D and a little bit Trivium, but also metal in general, but anything I do seem forced and too much alike these bands I mentioned.
At last I would like to ask: I have heard that working with other people may help, so how much theory do I need to know before assembling some jam partners og trying to forge a band?
Thanks in advance!
Technically? You don't need any theory before working with other musicians. It helps, but it's not required.
Songwriting and riffwriting like anything takes practice. What you need to do is pick out exactly what it is you like about those bands, and start coming up with stuff that fits what you like about those bands. It doesn't mean you'll come up with your best track straight away (it was around 4-5 years of playing before I came up with anything that I still consider good today), but you'll start to notice what you like and what you don't like. Over time, you'll hear what you can do better, and you'll pick up your own style. My style is quite identifiable in its influences, but at the same time it's not like anyone elses because I've used my influences with my own interpretation of how to play to create it.
Something like Guitar Pro, or having a way to record and add drums is a good way to go, as you can lay a foundation down to play over rather than randomly playing. In Guitar Pro too, you can pretty much write without even picking up an instrument, and then work at being able to play it (I often make things in Guitar Pro that are a bit beyond me, but not by a huge amount, give it 6 months and my playing is better as I can play what I've written).
It's not often the first thing you come out with will be anything good. Even the bands with great debut albums, they've usually been working on them for a couple of years or longer. Children Of Bodoms first album came around 4 years after they first formed (discounting the Inearthed EPs etc), In Flames 3 years, these things don't instantly happen.