how do u find chords of a particular song??

I find chords of a song by ear. Listening to it over and over until you get the pattern. Try it, your ears will become familiar with the chords in no time if you practice this.

I dunn have perfect pitch anyway... but usually to find chords or scale, first I find the scale.. by trial and error... then If I've found the scale, the chords is easy to get.. :)

practice!....its called "Aural Awareness"...you keep practicing..eventually..you just know...practice scales...stuff like that

Do you mean when writing original material or when playing cover songs from other band. I have found that just memorizing the many scales and knowing which key they are in I can improvise as long as the song is in the same key, There are several tab program out there that can let you know the types of scales and maybe some more techniques or practice lessons.