It's important to recognize that James is unlike most of Paul's epistles. James, while a letter (James 1:1), is a book of wisdom in the category of the books of Proverbs or Ecclesiastes.
The prologue (James 1:2-8) introduces wisdom in exactly the way wisdom literature would: "If any of you lack wisdom, let him ask of God, that giveth to all men liberally, and upbraideth not; and it shall be given him." Notice the characteristics of identifying the practical need and the practical mechanism to resolve the need. Notice as well the method of argumentation supporting the practical instruction. It can be illustrated in this form (James 1:5):
Need | If any of you lack wisdom,
Technique | let him ask of God,
Argument 1 | [God] giveth to all men liberally, and
Argument 2 | [God] upbraideth not; and
Solution | it shall be given him.
We see James use this form or similar forms throughout the book. For example, in the very next maxim, James writes (James 1:6-8):
Technique | But let him ask in faith, nothing wavering.
Argument 3 | For he that wavereth is like a wave of the sea driven with the wind and tossed.
Result | For let not that man think that he shall receive any thing of the Lord.
Argument 4 | A double minded man is unstable in all his ways.
The remainder of the book tends to address the same issues at the prologue, though in greater depth, with the same wisdom-genre emphasis on holy living.
James 1:9-15 is a discourse on the temptation issue mentioned in James 1:2-3.
James 1:16-18 is a discourse on the God's gift issue mentioned in James 1:5.
James 1:19-4:12 are discourses on holy living with frequent returns to the issue of double-mindededness. James 2:14-26 provides a special case with respect to faith, that we will discuss in more detail in another post, Lord Willing.
James 4:13-17 and 5:1-6 are two calls of condemnation on the presumptuous rich.
James 5:7-8 and 9 are two encouragements to the brethren to holy living in view of the Lord's imminent return.
James 5:10-11 is an exhortation to endure trials/temptations harkening back to the James 1:2-3 and James 1:9-15 points.
James 5:12-18 are more encouragements to holy living.
Finally, James 5:19-20 is particularly an encouragement to assist other brethren in holy living.