As Kidner puts it, "They are in double harness, rather than in competition." Rather look for the ways that second idea builds upon the first. The idea in the first line is contrasted or negated in the second line as a means of reinforcing it.It is found most commonly in the Proverbs and in the didactic psalms.
But scholars have realized rather recently that synonymous parallelism is something of a misnomer. You might describe it as "A, what's more B." The second line always seems to carry forward the thought found in the first phrase in some way.
This progression is sometimes subtle, but often quite obvious.
The Psalms express the entire spectrum of human emotion -- fear, despair, longing, love, hope, joy, and exultation.
They also instruct us in how we can voice our own prayers and praise to God.
In addition to these two common forms of Hebrew parallelism, scholars have found a number of other less prominent varieties.