Question about scales

[total_newb]

I noticed in one of Bernhard's posts that he has his students practice a scale that goes along with the piece they're working on (specifically referring to Gymnopedie). My question is, how do I know which scale I ought to practice alongside of a piece I'm practicing for that session? For example, I'm learning Russian Folk Song (which starts out b-d-d-d). How do I decide which scale to practice with?

Thanks!

[outburst]

I don't know the piece you are referring to but to find the scale you want you need to look at key signature.

The key signature appears right before the time signature. Since I believe you have just started playing the piano it probably is C major.

[total_newb]

Ah, thank you! Key signature! I was wondering what that was useful for..now I know.  

ETA: Do you have to just use the circle of fifths to find the key signature? I looked and was able to figure it out using this chart, but is that the most efficient way? I guess after a time you just memorize it.