Depending on how low-level and how much optimizing your group does...
It may not be necessary.
The monk, overall, is a very poor class. But the first and second level of monk easily keep pace with other low-tier warriors, and at these levels, while spellcasters can generate distinct statistical advantages for themselves if they are clever, their true dominance is several levels away.
So if you stop before, say, level 6, and the party doesn’t optimize particularly hard, the monk is probably fine even as-is.
Increased starting ability scores is a reasonable approach to some issues, however.
Many of the monk’s problems stem from the fact that he doesn’t just want decent, he wants good scores in more abilities than are typically tenable. Ideally, his Strength, Dexterity, Constitution, and Wisdom are all 14 or greater, and his Intelligence is not below 10. And some of those abilities have to be higher than that, though which ones will depend on the build.
So if you give the monk high enough ability scores to have 14-18 in four different scores, say something like an 18, 18, 16, 14, 14, 8 array, he’s in a much better position. Personally, I’d prefer to cut down on the MAD by reducing the monk’s need for all of this, but simply giving higher ability scores can work, at least at low levels. Eventually the monk will start to suffer from the expense of improving each of these scores, but that happens well after the monk starts having bigger problems.
Speaking of bigger problems, be aware that numbers are not the entirety of the monk’s problems. He has numerical problems, but even if you get around them, the monk is still fairly mediocre (again, considered as a whole; the first two levels are fairly good). If you get to 6th or 7th level, the monk is going to suffer simply because he does not have particularly useful or potent class features. Or, the ones he does have, are very strictly limited, or were gotten at level 1, and while very good then, the stagnation since then is a problem. These issues are not solved by giving high ability scores. These issues are solved by accepting that the monk class was a design failure, and replacing it with something better. Cleric, psychic warrior, and swordsage (each mystic warriors based on Wisdom) are my usual go-tos.
Risks
There are risks here. Especially at the very earliest levels, when the monk doesn’t need that much help (at least relative to fighters, paladins, rangers, and rogues), he’t going to look pretty sweet, with good AC, great saves, decent enough attack, with two attacks, and decent damage. Plus maybe a combat maneuver up and running.
But even more significant is out of combat. With high enough scores to have a decent Intelligence, a halfway-decent 4+Int skills, a fairly solid class list, and around-the-board high ability scores, the monk is going to be good to great at lot of different skills. He probably won’t be as good a sneak as the rogue, but he’ll be able to keep up. He probably won’t be any kind of face, but lying to him at this level will be very difficult. Balancing, climbing, jumping, those sorts of things, he’ll be very good at.
Depending on how important skills, particularly exploration/navigation skills, are in your game, the monk just might end up seeming like he’s fairly good at everything. If your group doesn’t optimize much, and this doesn’t get beyond like level 5 where skill ranks start to dominate the skill conversation. Just something to consider.
