First, make sure that Charm Person is one of your first spells
Then, charm an archer or a heavily armed warrior to be your meat shield. Or charm two of them.
I learned this trick in Original D & D; a friend of mine had, early in his adventuring career, charmed two warriors (2d level fighters) that the party had encountered during an early random encounter. They stayed charmed.
For the first few months of that campaign, the charm did not break. (Using the Intelligence table in Greyhawk). He was wise enough to do his best to keep them alive, and as NPCs they got a share of XP and ended up leveling up with the party. (Yes, there was some grousing among a few of the party members, but so be it; the Magic User survived and was able to cast that oh so precious spell when it was needed by the party).
This powerful version of the charm person spell carried over into AD&D 1e.
As powerful as sleep, in some regards; Charm Person was all or nothing
When we look at Charm Person in D&D 5e, it is pathetically weak.
In its AD&D 1e form, it is similar to the Dominate Person spell, or 3.5e's version of Dominate Person. The below description, edited, required me to combine the 2d level Druid version of the spell and the 1st level M-U version of the spell to demonstrate this feature: the table was in the Druid section. The MU spell is the same as the Druid version (mostly, but no beasts could be charmed by an M-U) per PHB p. 65 (table is from PHB p. 55). (I subbed in caster for magic-user or druid to make this more coherent)
Charm Person (Enchantment/Charm) / Level: 1
Components: V,S / Range: 12''
Duration: Special {Italics Mine}
Saving Throw: Neg. {means saving throw negates effect}
Area of Effect: One person
Explanation/Description: {snip} ... the {caster} can charm only persons, i.e.
brownies, dwarves, elves, gnolls, gnomes, goblins, half-elves, halflings, half-orcs, hobgoblins, humans, kobolds, lizard men, nixies, orcs, pixies, sprites, and troglodytes. All other comments regarding spell effects apply with respect to persons.
The creature then will regard the {caster} who cast the spell as a trusted friend and ally to be heeded and protected. {italics mine} The spell does not enable the {caster} to control the charmed creature as if it were an automaton, but any word or action of the {caster} druid will be viewed in its most favorable way. {italics and bolding mine} Thus, a charmed creature would not obey a suicide command, but might believe the {caster} if assured that the only chance to save the {caster}'s life is if the creature holds back an onrushing red dragon for "just a round or two". Note also that the spell does not empower the {caster} with linguistic capabilities beyond those he or she normally possesses. The duration of the spell is a function of the charmed creature's intelligence, and it is tied to the saving throw. The spell may be broken if a saving throw is made, and this saving throw is checked on a periodic basis according to the creature's intelligence:
\begin{array}{r|lll} \text{Intelligence} & \text{period between checks}
\\ \hline \text{3 or less} & \text{3 months} \\ \text{4 to 6 }
& \text{2 months} \\ \text{7 to 9 } & \text{1 month} \\ \text{10 to
12} & \text{3 weeks} \\ \text{13 to 14} & \text{2 weeks} \\ rest &
snipped \end{array}
{snip} If the recipient of the charm person/charm mammal spell makes
its saving throw versus the spell, its effect is negated.
Most NPC Fighting Men didn't run around with a 19 intelligence. If one spoke Dwarfish, one might charm a dwarf into service.
Second: charm a martial NPC
Charm a warrior, Orc, dwarf, whomever you meet. They are your personal protector and body guard, a martial character that you control (by giving rational orders to) in the same way that you could roll for what your henchmen do. (Most DM's would have you roll their attacks, etc).
The key advantage is that this henchman does not need a morale check, nor cost money in pay. This charmed NPC needs periodic saving throws versus the charm person spell. In two months time, you'll probably have gained a few levels - if you survive. There are still ways to get killed, like dragon breath, falling into traps, exploding poison gas from a trap triggered by the thief, orc archers, etc.
Third: go adventuring!
You need to remember that this NPC is charmed by you and is not an automaton, but as it usually works out in play you can give them reasonable orders and they do your bidding. Each day, as you prepare a spell, you figure out which of the few in your book that you need. You don't need to keep charm person prepared for this to maintain its effect. If you want to charm another NPC, well, go ahead. Just be ready for what happens when the charm wears off - shennigans abound!
Or, release them from your service before that happens.
This answer is related to Daniel R. Collins' answer about henchmen, but it is also a different way to play a minion-mancer kind of character; in this case, you charm normal NPCs who become your minions, rather than undead or beasts.
When a Druid caststhis spell on a beast as a second level spell, they could get, for example, a grizzly bear or a wolf, or an alligator - that beast would stick around for a while.
Some things for a Magic User to do in combat include ...
Hold the torch so that the humans can see; light the flasks of oil that your henchman or party members throw; throw burning flasks of oil at the enemy; throw darts; watch for flanking by the enemy; drag downed fighters out of the fight; in general use your brain to think up clever things for your party to do and shout it out as a suggestion, and if you have one, administer a healing potion to your comrades so that they can keep fighting.
Use your wits to improve the party's chances for success.
One of our Magic Users at low level (we were in the Caves of Chaos) tried to make a lasso (we all carried 50' of rope, it was a thing back then) to toss at an enemy to try and restrain him. It didn't work, but it was worth trying. Another time it was our Magic User who held the other end of a rope; the party began to withdraw and the goblins ran after us. Most of them tripped over the rope ... so the thief tossed a flask of flaming oil at the pile up.