how do i have a higher chance to inflict status affect on enemy?

You need to increase your faith stat. There was reddit post from a jp player who explained it.

I'm sorry I'm not sure at this point. Leveling Ninja's Poison Mist increases it's Poison effect but I think it means the damage of Poison and not the chance of inflicting Poison.

You can check the resistances of an enemy during battle. Use abilities inflicting Poison to enemies that have weak resistance to the status effect.