Yeah, on "quaalude" the strings come in nice, at a good moment, starting on a nice interval. They soon start losing their focus, however, and there is a way to avoid that. Mute everything but the electric piano and the stringline and have a listen. The electric piano, being the primary instrument, and the thing you wrote the song around, is providing the modal basis for everything else... It's laying down the rules that all the other instruments have to obey. In this case, they're laying down the rule that the chords move from D minor to C major to B flat major. That means that if you're writing a melody line, or a guitar solo or whatever, you're obligated to either avoid or honor the major or minor third (The "Mi"). On the D minor chord the "Mi", (otherwise known as the 3rd) must be flatted, because a minor chord is defined by having a flatted 3rd. On the C and the B flat, the chords are major, so the "Mi" must not be flatted. To find the "Mi", just play a major scale... Do Re Mi Fa Sol La... etc... (In the key of C the major scale is just all the white keys in a row.)

From a root note of D the "Mi" or major third is F sharp. Your electric piano chord is D minor, which you remember is defined by its third being flatted, or lowered a half-step. therefore any time an F sharp is played over a D minor chord it will be a glaringly wrong note. Replace it with the flatted 3rd, in this case being F.

Conversely, your C chord is major. The 3rd of C is E. So anytime an E flat is played over that chord it will sound glaringly wrong, and will throw the listener out of the track. On the B flat the 3rd is D. So any time you play a D flat over a B flat major chord it will sound glaringly wrong.

I hope that doesnt seem too hard to understand. It's really pretty simple when you just play it.