In My Opinion
По мом мишљењу — State, soften and defend an opinion without sounding blunt.
What you think
«Мислим да…» introduces an opinion. «По мени» is shorter; «по мом мишљењу» is more deliberate. All three take a complete thought after them.
Мислим да је књига боља.
I think the book is better.
Agreeing with someone
«Слажем се» means I agree. The person follows са + instrumental: слажем се с тобом, с Аном, с професором. Negation stays separate: не слажем се.
Слажем се с тобом.
I agree with you.
Right — but gently
«У праву си» means you're right; formally, «у праву сте». To disagree without closing the conversation: «Не слажем се, али разумем зашто то кажеш.»
У праву си, али имам једно питање.
You're right, but I have one question.
The confidence dial
можда (maybe), вероватно (probably), сигурно (certainly). «Чини ми се да…» — it seems to me — is a useful hedge, with the familiar dative clitic ми.
Чини ми се да ће падати киша.
It seems to me that it will rain.
Put the small word early
Serbian clitics lean toward the second position: «С њим се не слажем.» The opening phrase с њим takes focus; се follows it immediately.
С њим се уопште не слажем.
I don't agree with him at all.
Put It Together
Keep the lesson goal in view: State, soften and defend an opinion without sounding blunt. Revisit the examples, then test yourself in practice.