"Hey There" is normally played as a ballad. This time, the melody goes at medium balled tempo, but the band is playing an energetic funk groove. This lends itself to a higher energy improvisation.
This is a relatively easy song to improvise on. But there are some complications. One of the most basic things the soloist must do is know the song form !!!
This seems like a simple song form, but it isn't. I would call it A-A'-A-B with a tag. The first A section is simple, predictable chords I-iv-ii-V7 and so on like a million doo-wop songs. That is in Eb concert. The next 8 bars (A') are basically the same, but now up a major third into G major concert. No problem if you know your Eb and G scales. And the third group of 8 bars is back to Eb, just like the beginning. That is straightforward.
Things start to deviate from the common song forms in that B section starting at bar 25. Bars 25-28 can be thought of as an "interstitial" -- a little phrase that connects two different parts of the song. The final section really starts at at measure 29 (the lyrics are "Or are you not seeing things too clear? Are you too much in love to hear? Is it all going in one ear and out the other?") The music is different in that final section and so are the lyrics. Before that, the singer is trying to give advice to the would-be lover. At bar 29, the singer is giving up hope that his advice will be heeded and basically washes his hands of the matter. You can incorporate these emotions into your solos. Measures 1-28 are hopeful that the lover will listen. Measures 29 to the end are resignation, "C'est la vie".