I thought upon my ways [1] The amount is, that after the prophet had paid due regard to his manner of life, his only aim then was to follow the teaching of the law. In these words he intimates indirectly, that if it be inquired why men go astray, and are miserably distracted amidst conflicting impulses, the reason is, their thoughtlessly indulging themselves in the gratification of their passions. Every man watches most carefully, and applies all his energy to whatever his inclination may lead him, but all are blind in choosing the object which they ought to pursue; or rather, as if their eyes were sealed, they are either hurried away inconsiderately, or else, through carelessness, wander imperceptibly from one object to another. One thing is certain, that there is no one who carefully considers his ways; and, therefore, it is not without reason the prophet exhorts us, that the commencement of a godly life consists in men awaking from their lethargy, examining their ways, and, at last, wisely considering what it is to regulate their conduct properly. He next instructs us, that when a person is inclined in good earnest to frame the course of his life well, there is nothing better than for him to follow the direction which the Lord points out. In fact, were not men infatuated, they would universally and unanimously make choice of God to be the guide of their life.

Footnotes

1 - "I thought on my ways chsvty, chashabti, I deeply pondered them; I turned them upside down: I viewed my conduct on all sides. The word as used here is a metaphor taken from embroidering, where the figure must appear the same on the one side as it does on the other: therefore the cloth must be turned on each side every time the needle is set in, to see that the stitch be fairly set. Thus narrowly and scrupulously did the Psalmist examine his conduct; and the result was, a deep conviction that he had departed from the way of God and truth." -- Dr Adam Clarke

I thought on my ways - This language most naturally refers to the time of conversion, and may be employed without impropriety to describe the process of a sinner's turning to God. It would seem to be descriptive of the experience of the author of the psalm when he became personally interested in the subject of religion. The first step in such a work is reflection on the course of life which has been led; on the guilt of such a course; and on the consequences. It is a pause in the career of sin and folly - a pause for reflection and thought. Compare Luke 15:17-18. No one is converted without such reflection; and as soon as a sinner can be made to pause and reflect on his course, there is hope that he will be converted. Assuredly it is proper for all, whatever may be their circumstances in life, to pause from time to time; to reflect; to ask what will be the consequences of the course of life which is pursued.
And turned my feet - Changed my course of life. He himself did this in fact; and he does not hesitate to say that it was he who thus turned. His own agency was employed. He does not say that he "waited" for God to turn him; or that he found he could not turn of himself, but that he turned; he paused; he reflected; he changed his course of life. This is true in conversion always. There is an actual turning from sin; an actual turning to God. The sinner turns. He leaves an old path, and treads a new one. He does this as the conscious result of reflection on the course which he was pursuing; and there is nothing in his actual turning, or in his whole future course, which is not the proper result of reflection, or which a proper reflection on the course of life would not lead to and justify. Man himself is always active in conversion. That is, he does something; he changes; he repents; he believes; he turns to God; it is not God that changes, that repents, that believes, that turns; it is the man himself. It is, indeed, by the grace and help of God; but the effect of that grace is not to make him idly wait; it is to rouse him to effort; to lead him to act.
Unto thy testimonies - Thy law, considered as the divine testimony in regard to what is right.

First. I thought on my ways - חשבתי chashabti, I deeply pondered them; I turned them upside down; I viewed my conduct on all sides. The word, as used here, is a metaphor taken from embroidering, where the figure must appear the same on the one side as it does on the other; therefore, the cloth must be turned on each side every time the needle is set in, to see that the stitch be fairly set. Thus narrowly and scrupulously did the psalmist examine his conduct; and the result was, a deep conviction that he had departed from the way of God and truth.
Secondly. And turned my feet unto thy testimonies - Having made the above discovery, and finding himself under the displeasure of God, he abandoned every evil way, took God's word for his directory, and set out fairly in the way of life and salvation.

I thought on my (b) ways, and turned my feet unto thy testimonies.
(b) He shows that no one can embrace the word of God, unless he considers his own imperfections and ways.

I thought on my ways,.... What they were, whether right or wrong; whither they led, what would be the consequences of walking in them: the Septuagint and Arabic versions read, "thy ways"; no doubt the psalmist thought of both; of his own ways, in which he had walked; and of God's ways, which he directed him to walk in: and, considering the superior pleasure and profit of the latter, he preferred them to the former. The Targum is, "I thought to mend my ways", or "make them good". Hence he took the following step:
and turned my feet unto thy testimonies; betook himself to the word of God, which testifies of his will, and directs to those ways he would have his people to walk in; and he steered his course of life and actions thereby; he turned from his own ways into the ways of God; under the influence of divine grace, he turned, being turned.

So the prodigal son, when reduced to straits of misery (Luke 15:17-18).

Thought - I seriously considered both my former courses, and my duty in all my future actions.