James deals with three areas of a normal Christian's life - suffering, happiness and sickness. To each of these he applies a correct response:

Suffering - pray
Happiness - sing
Sickness - call for elders

SUFFERING can mean many things. It covers everything from poverty to persecution, bad luck to any of those things that spoil life. Everybody has a different definition for 'suffering' because we all live in different circumstances.

HAPPINESS can also come for many different reasons. It may be a birthday, a meal, a scene, a movie. When we are happy, James tells us to sing.
SICKNESS can be caused by several different things. James mentions three reasons for sickness and gives us a course of action for each:
1. Literal sickness, caused by germs or virus. After prayer, if God wills, the sickness will go away.
2. Sickness caused by sin. Many sicknesses are the result of sinful habits, or even of someone else's sin. It is important to deal with the sin as well as the sickness it may cause.
3. The 'sickness' of bad relations with other Christians. These need to be 'healed' as well.

prayed for a drought, and then for rain. In both prayer! he was heard.

Elijah was used to having his prayers answered. He had built up a close relationship with God over many years, so he knew God well enough to expect an answer. This is why "elders" are called for by the sick Christian. These people should be experienced, and quite used to seeing God answer prayers.