Below I divide the time that you sing a song and accompany yourself on the piano in 4 phases:
PHASE 1: You play an introducing piece on the piano.
Summertime on piano with melody.
PHASE 2: As soon as you start to sing, you start to play differently, according to the points a through h below.
Summertime on piano with only chord for voice.
a) You start to play easier with fewer chords, in order to let your singing BETER UIT DE VERF KOMEN and to be not distracted by playing the piano while you sing.
b) You play the chord therefore best in a simple position.
c) You only use the bass tone and a chord (so not a bass with more then 1 tone)
d) You sing the melody of the song with your voice and don't play it on the piano.
e) You play softer now, adapted to the volume of your voice. The trick is: playing the piano softly and singing loudly.
f) If you want to ask the attention for a word in the text you sing, you play one tone loudly or softly for example, in order to continue your text from there.
g) If you want to draw the attention for the text you sing, you sometimes keep silent, to increase the tension, while you continue playing on the piano meanwhile.
h) Your words have to express itself to the background of your piano-playing (for example the phrase ''hush little baby'' in the song 'Summertime' you will perform soft, tender and comforting)
i) You look slantly over your shoulder to the people that listen, for you sing words with a meaning and you bring the people a message.
j) You sing well and convincing and play the piano in a way that make your singing sound better.
k) And of course it is necessary that you know the text of your song by heart.
PHASE 3: You play a piece on the piano, sing a bit and use your voice in an instrumental way, without words, as if it was a second instrument with which you work (this is called 'scatting'). Looking slantly over your shoulder to the public is not necessary now, because you don't have a text and just improvise on the piano with your voice accompanying it.
PHASE 4: You also conclude with a piece of piano-playing.
The phases 2 and 3 can be repeated.
(Finally: in case you might play a Son and want to give extra atmosphere to it, you can accompany your piano-playing by singing with your voice and making sounds to inspire the people to dance.)
Summertime (Book: Am6 E7/B Am6/C, ...E7/B Am6 Dm F, FM7 D#dim E B7, .... did not suite me)
Summer[Em]time [B7][Em]
And the [B7] livin' is [Em] ea[B7]sy [Em]
Fish are [Am] jumping [F#7]
And the cotton is [B7] high [C7][B7]
Oh, your daddy's [Em] rich [B7] [Em]
And your [B7] ma is good [Em] looking [B7][Em]
So [G] hush little [A7] baby
[B7] Don't you [Em] cry [B7]