Strengthen yourself in the Lord

I often feel weak. It is noticeable. Palpable. It is impacting nearly every aspect of my life. I want to be strong, but I also want God's strength to be manifest in my own weakness.

I am intrigued by this verse in 1 Samuel 30:6:

And David was greatly distressed, for the people spoke of stoning him, because all the people were bitter in soul, each for his sons and daughters. But David strengthened himself in the Lord his God.

What does it mean to strengthen yourself in the Lord? How does one do that? Perhaps it simply means that we engage in our personal favorite practice that brings us the most joy in the Lord. For David, that might have meant writing a poem or a psalm.  I'm not sure what it means for me.

But then we see this in 1 Samuel 22: 35-43

He trains my hands for war,    so that my arms can bend a bow of bronze.
You have given me the shield of your salvation,
    and your gentleness made me great. You gave a wide place for my steps under me,
    and my feet did not slip;
 I pursued my enemies and destroyed them,    and did not turn back until they were consumed.
 I consumed them; I thrust them through, so that they did not rise;
    they fell under my feet.
 For you equipped me with strength for the battle;    you made those who rise against me sink under me.
 You made my enemies turn their backs to me,
    those who hated me, and I destroyed them.
 They looked, but there was none to save;
    they cried to the Lord, but he did not answer them.
 I beat them fine as the dust of the earth;
 I crushed them and stamped them down like the mire of the streets.

Whatever David did to strengthen himself in the Lord, he was willingly boastful about what it meant for him in battle. I want to have a zeal for battle like this.