Something I do (for some songs), is do a simple intro (which could be the last 4 or 8 bars of the song, or some other simple chord progression that leads to the first chord in the melody). ... and what I try to do is, in the last measure before the singer starts, is to play a run or arpeggio that ends on the note that the singer starts on. That way, it sort of "gives a hint" of what that first note will be, a little before the time she has to sing it. I think 'rosetree''s suggestion is similar, this is just my 'spin' on it :-)
Accompanying singers is a wonderful thing - one of my favorite things to do musically speaking!
Jim
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Genos / Tyros5 / HK Lucas Nano 600 / FTB Maxx 40a / EV ZX1A / Rock'n'Roller cart / Hauptwerk virtual pipe organ / misc other audio & music toys