An opinion becomes an argument once you link your points. These connettivi do the linking:

Connettivo	Meaning	Job
infatti	indeed, that's right	confirms
anzi	on the contrary, in fact… even	corrects and goes further
invece	instead, whereas	contrasts
però / ma / tuttavia	but / however	objects
d'altra parte	on the other hand	weighs up
quindi / perciò	so, therefore	concludes
inoltre	moreover, what's more	adds
comunque	anyway, however	moves on
insomma	in short, all in all	sums up
cioè	that is, I mean	explains

• «Fa freddo.» «Infatti, ho messo il cappotto.» — “It's cold.” “Exactly, I've put my coat on.”
• Il film non è brutto, anzi, è bellissimo. — The film isn't bad — quite the opposite, it's wonderful.