Soundproofing a flat

Hi
I have just moved to a flat in Barcelona and am struggling with the street noise and the rumble of the metro.
Does anyone know any good soundproofing companies and/or any DIY tips to reduce the noise. I live in Sants on the top floor but it is quite a low building compared to the others

Any help or advice greatly appreciated

Shaun

Draft excluder around the doors and windows usually works wonders.....and its cheap