how can a person from the general public contribute to country's
economy by being well-informed?
Primarily, by promoting policies and pursuing models which the informed person identifies as premised on realistic arguments versus those that are detrimental or make no sense.
A well-informed individual on his or her own is unlikely to outweigh activism or lobbying that pursues adverse interests. Nonetheless, that individual has more elements [than uneducated people] to scrutinize, analyze, and --if need be-- dismantle others' arguments. At the bare minimum, the well-informed individual can reasonably discern what would be most convenient (whether domestically or for the economy as a whole).
I understand one of the reason would be tax. If a person understands
the importance of paying tax, then the person would be understand his
responsibility and pay his tax promptly.
Not necessarily. Being well-informed is not deterministic of the rationale and conclusions at which the person will arrive. The well-informed person could reach a conclusion which is the opposite of the conjecture that he or she will become enthusiastic about taxes.
For instance, the individual could identify (as I personally do) that heavy taxation curtails a person's freedom, significantly complicates his or her financial planning, destroys incentives for productivity/innovation/self-improvement/etc., and even is ineffective toward the purposes of "well-fare" state with which politicians attempt to justify brutal levels of taxation.
Additionally, notions of utility as well as time value of money might still prompt a pro-tax advocate to delay his payment of taxes instead of paying them sooner.