John Gill Commentary 1 Samuel 18:5

"And David went out whithersoever Saul sent him, [and] behaved himself wisely: and Saul set him over the men of war, and it was good in the sight of all the people, and also in the sight of Saul`s servants." — 1 Samuel 18:5 (ASV)

And David went out whithersoever Saul sent him
About any business whatsoever, especially about martial affairs, for which he was abundantly qualified:

[and] behaved himself wisely ;
in the management of them, using great prudence and discretion, and so failed not of success, and of recommending himself; the Targum renders it "prospering"; he was prosperous and successful in whatsoever he engaged, for the Lord was with him, and blessed him:

and Saul set him over the men of war ;
that is, of some of them, gave him the command of a troop; for Abner was captain or general of the army, and continued so:

and he was accepted in the sight of all the people ;
of all the people in the land in general, of all that knew or heard of him; being looked upon as a wise, valiant, and successful commander, and which gained him the esteem and affection of the people:

and also in the sight of Saul's servants ;
which was very much, and a rare thing, for servants are too apt to envy such as are rising in their credit and reputation; though this must not be understood of all, without exception; but of the generality of them; nor is the word "all" used of them, as is of the people; for some of them took the part of Saul afterwards against David, and were secretly his enemies, see (1 Samuel 18:22–26) .