Keep the six-slot limit in mind
A run can carry up to three active abilities and three passive abilities. That limit means every choice needs a purpose.
Choosing an ability you already have upgrades it, so a focused build often beats a noisy build with too many unrelated effects. Repetition is not wasted when it makes the main pattern stronger.
Before picking a new icon, ask what job it does. Does it clear small enemies, protect your health, help you hit at range, or make the boss room shorter?
Use rerolls to complete a plan
Rerolls are best when you already know what is missing. If you need damage, look for a skill that improves clear speed. If you need survival, look for shields, range, or safer passive value.
Do not spend rerolls just because a choice looks boring. Save them for moments when the current options would pull the run away from its strongest pattern.
A rare special active ability can be worth bending the plan around, but only if the rest of the build can support it. A dramatic skill still needs enough survival and uptime to matter.
Build for the room you are losing
If normal rooms are the problem, choose skills that clear groups and reduce pressure quickly. If bosses are the problem, choose repeatable damage and passives that keep working while you move.
A good build is not always the loudest build. It is the one that answers the next few rooms without abandoning the hero's natural strength.