I'm playing a few years guitar now, but i always played the rythym parts/chords. i'm on a point now where i wanna improvise, but i'm facing a problem.

When i hear a song with pretty simple chords how can i know what scale to play to improvise over the chords.


Two ways come to mind off the top of my head. Learn how to find the notes of chords, look at all the notes, then :

http://en.wikipedia.org/wiki/Circle_of_fifths Know that. At some point you will have to do those things.

The other, is mostly listening. Listen to what chord it seems like the song sounds finished on. Combine that with knowing the roman numeral analysis which is this :

In any given key , the diatonic chords are as such

I ii iii IV V vi vii (halfdim)

Capital letters are major, small are minor.

They simply correspond to the notes in a scale, so the chords in C major are

C Dm Em F G Am B halfdim

A grouping of any of those chords means we are probably (I'm keeping it simply here) in the key of C.

Ok, now you try , I'm playing these chords

Dm F G C what key ?

how about

G Bm C D?

My thoughts are a bit scattered here but it should be enough to raise a few more questions in you.
Don't tell me what can not be done

Don't tell me what can be done, either.

I love you all no matter what.
You either identify the chords by ear or you write down the chords if you have a tab or something and figure out the key signature / scale from that.

There is no easy 'just do this in three easy steps' answer because it comes down from training your ears and knowing the basics of the Major scale & its chord relations.