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Encourage your players to let the narrative drive their choices during character creation, rather than what is the most "optimal" mechanical choice.
The problem with mechanical optimization in OSR+ is that while players can optimize their PCs for combat encounters or spellcasting or social interaction specifically, you as a GM design challenges in the adventure after the story hooks they developed in session zero, not their abilities. Therefore players who optimize for general button-pushing will not be best equipped to meet the challenges of the adventure.
What is Optimization?
Optimization in OSR+ only matters insofar as it helps the player achieve a character concept. Only in pursuing a character concept should players attempt to make optimal choices when choosing abilities. And what is a character concept, exactly?
Character Concept
A character concept isn't "the tank that takes the brunt of the damage" or "the face that handles the social encounters." A character concept is a "squirrelly but scholarly gnome on a quest to repair his master's Clockwerk android" or "a magical musician who carries the song of her people after her hometown was destroyed in a cataclysm." These are characters whose abilities are chosen to reflect their narrative agenda, and for whom the choices players make about what they can do will be meaningful in the context of an adventure.
Example 1: The Squirrelly Gnome Scholar
The gnome could be played any number of ways: as a Nim Daredevil Artificer with a decent Smart to reflect his intelligence, a high Deft to reflect his squirreliness, and a low Mighty to reinforce his Foolish flaw (which manifests as cowardice). Or you could play him as a Nim Mage Wizard with an extremely high Smart and 0 Mighty, who collects magic scrolls in search of that perfect spell that will restore the android to life (perhaps he takes the conflict The Overachiever).
Such a character concept could benefit from making story tags that reflect his expertise in repairing Clockwerk or performing scholarly research, the former of which naturally synergizes with the Nim's advantage on Deft, and the latter of which would bolster an already maxed-out Smart check.
Example 2: The Musician Survivor
Similarly, what kit or class you choose for the musician depends on how you want to play her. If the player is a Collaborator who enjoys supporting her party members, a Bard Skald might be a good choice because the kit requires coming up with tall tales in exchange for status effects. If the player imagines a strong-willed rockstar musician with a fierce song, perhaps a Psychic Spellsinger makes sense, since Psychics rely on Mighty for their spells.
In both cases, story tags that reflect the character's experience as a survivor would benefit from their likely middle-to-high Mighty attribute.
Modularity
As you can see, there aren't "wrong" choices when it comes to putting together a character in OSR+; the system was designed to be modular in a way that makes mixing and matching interesting and fun. The key to building a successful character in OSR+ is leading with the concept when making mechanical choices. The rest will naturally follow.
Party Composition
OSR+ doesn't have the same concerns with regard to party composition that other games have.
It doesn't matter if everyone in the party is playing a healer, or if the party has no healer, or if none of the "healers" can actually heal things. This is because there are many different ways to conceive of a "healer," and unless two players are making exactly the same choices during character creation, they won't end up with the same PC in the end.
For example, consider all the below character concepts that take the Cleric class. The class itself relies on Deft for its spells, but also Smart for its maleficence. Add to this that you must factor in origins that may impose advantage or disadvantage on attributes.
Cleric Necromancer
Necromancers are all about control, as their Animate Dead ability demonstrates. But most Necromancy spells rely on Thaumaturgy (Deft) or Psionics (Mighty), which may steer a player to focus on those attributes over Smart. At the same time, the Necromancer is an oftentimes gruesome bookworm, so story tags like Occult Knowledge or Vivisector might help with those Smart checks when he's in the lab crafting his twisted creations.
Cleric White Mage
The White Mage exchanges spells she knows for spells of the Curative school, which all rely on Deft. Such a character might be a devoted pacifist with a 0 Mighty and the Divine maleficence, specifically to use magical harm against the Undead monster type. She might not even know how to fight, taking skills like Lore and Domain Knowledge (Herbalism) over any weapon skills.
Cleric Inquisitor
Inquisitors tend to be stern, judgmental, and strong in their demeanor or physicality. You might forgo book knowledge to rely on instinct and strength, taking a higher Mighty and Deft score than Smart. Donning a little bit of armor and knowing how to use a Flexible weapon might be worth it to back up the kit's intimidation ability with the threat of violence.
Cleric Monk
In OSR+, Monks are competent fighters who know how to mete out justice to whole crowds, thanks to their ability to explode on a 5 or a 6 and spread damage against a number of targets in unarmed combat. A Cleric Monk might try to keep attributes balanced, while relying on spells like Enchant Weapon or Mystic (Grace / Intellect / Strength) to excel with divine inspiration when the situation calls for it.
Cleric Druid
Druids are typically conceived of as wise priests of the natural world. The Druid's ability to shapeshift can complement any take on the Druid as a concept, but stealthiness is an angle not often considered. For example, imagine an urban druid who shapeshifts into rats, raccoons, and bats. His Deft might not represent wisdom, but natural instinct mixed with animalistic reflexes. Skills like Reflexes, Survival, and Trade (Black Market) might be vital for surviving in a dangerous city.
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