Songwriting. Tips/Advice?

I have been playing guitar for nearly 6 years now and I am in a band too. I now want to start writing my own songs instead of playing others bands/artists. I am into bands and artists like The Script, You Me At Six, All Time Low, Robbie Williams, James Morrison... Could anyone possibly give me tips on how to start out and what sort of things I have to do in order to write songs! Also I would also like to hear from people who write their own music how they are insipired to write their music. It would also be great if anyone could post on here some of their own lyrics, I promise I will not steal them! Many thanks.