I can easily just think of a riff then play it out on guitar, or listen to a riff and play it out on guitar (sometimes takes me a while if its a bit complex or something is hard to hear, but generally I can do this)

So If I want to write a riff, i will basicly try to think of it in my head, then just play it, but all the riffs I have been playing suck hard, I just wanna write a simple nice sounding riff (wether its rock/blues etc. I dont mind, I just play whatever i feel like playing)

So, any tips on getting inspiration for a good song?
I cant even think of any progression to use
what i do is listen to music and usualy it will inspire me and i'll hear riffs in that style in my head, i then just grab my guitar and try to replicate the riff i heard.
what you've got to remember though is that like everything practice makes perfect, no ones writes whole lotta love first go.
My ear is not trained particularly well, which can hold me back when trying to work things out by ear (obviously). However, if I hear a piece of music I like the sound of and it inspires me to write a piece of music inspired by it; I just try to imagine how it's played and then I play it. It's hit and miss, but I've written my favourite material this way. As my ear isn't trained to the level where I can hear what is going on, theory wise, there is little chance of me just re-hashing the inspiration. There is nothing wrong with stealing ideas, so long as you make them your own.