The purpose of a pianist when accompanying a singer is to provide support and a foundation to the soloist. Unlike playing in an orchestra where the piano is usually predominant, the piano is the background and is there to make the soloist sound as beautiful as possible. This may seem like a menial task, but in reality it is important and rewarding.
In order to learn how to accompany, there are a few basic steps to master.
1. Do Not Play the Melody
The soloist is already singing the melody. Consequently, if you're playing the melody as well, you will compete with the singer, rather than accompany. Since the voice can sing only one note at a time, it's your job as the pianist to provide the harmonies. In this way youre decorating the melody rather than duplicating and perhaps bogging down what is being sung.
2. Provide the Harmonies
Most likely, your piano teacher will include basic theory into your lessons. While it may not be the most interesting part, it is essential. From theory you will learn about the basic piano chords in a key I, IV and V7 as well as simple chord inversions. This is your groundwork in creating a piano accompaniment. Chords will harmonize with the melody, giving fullness and depth to the song. Practice to become easily familiar with the chords, switching from one to another and inverting them. Train your ear to hear when you need to switch chords to best go with the melody. Practice by humming the song while just playing the chords. Experiment until you get the best sound. The majority of songs both start and end with the I chord and progress next to the IV chord. If neither of those sound good as you're playing, progress to a V7. At first, this trial and error experiment can get frustrating, but persistent practice and more training will get you easily accustomed, and putting the right chords together will be simple.
Your left hand will provide the bass, while your right hand will be predominately piano chords. The left hand bass can be one bass note, or it can be added to by creating octaves. Look at your chord. The bass note you play in your chord will work as your left hand bass note. You can also split the chord up into both hands, or play broken piano chords. A broken chord is just what it sounds like; each note is played separately (or broken up) instead of together.
3. Pay Attention
Keeping an attentive ear is vital to accompanying well. Listen to the soloist's style, breaths and feeling. Each will dictate how you need to respond. Pause ever so slightly in appropriate places if the singer needs an extra breath. Increase or decrease dynamics when he does. Allow the singer to sing freely by being his follower, not his leader.
Be familiar with the song beforehand and be comfortable with the lyrics. Keep a copy of them in front of you to better follow the singer along. Always get together to practice before a performance, so you can interact well with each other. Each soloist has his own style of singing, so each time you accompany, the experience will be different. The basics, though, will always be the same.
The Mastering Piano Accompaniment course will teach you many techniques and styles that will help you become a better piano accompanist.