There are many ways to give your opinions when speaking English. The exact English expression you use depends on how strong your opinion is.
Giving your opinion neutrally
“I think…”
“I feel that…”
“In my opinion…”
“As far as I’m concerned…”
“As I see it…”
“In my view…”
“I tend to think that…”
Giving a strong opinion
“I’m absolutely convinced that…”
“I’m sure that…”
“I strongly believe that…”
“I have no doubt that…”
“There’s no doubt in my mind that…”
English expressions for asking someone’s opinion
“What do you think?”
“What’s your view?”
“How do you see the situation?”
“What’s your opinion?”
Talking about your beliefs
“I believe in…” (the importance of free speech)
“I’m a (great / firm) believer in …” (fresh air and exercise)
“I’m convinced that…” (there’s a solution to every problem)
“I’m passionate about…” (human rights)
“I’m committed to … ” (working towards peace”)
“I don’t believe in …”
“I think that … is” (true / complete nonsense, etc)
Note
After a preposition such as in or about, you need either a noun or a gerund.
For example: “I believe in free speech“, or “I believe in saying what you think”.
After “that”, you need a clause.
For example, “I believe that we must safeguard the planet.”
Giving a reason for your beliefs
“There must be / can’t be .. (life after death) because otherwise…”
“There’s no evidence for / to support …” (an afterlife)
“There’s no other way to explain / account for …”
Talking about your religious beliefs
“I’m a practising …” (Catholic, Muslim, Jew etc)
“I’m a non-observant / lapsed …” (Catholic)
“She’s a devout…” (Christian, etc)
“I’m a ‘don’t know.'”
“I’m an agnostic.”
“I’m an atheist.”
“He’s an extremist / fundamentalist / evangelist.”
Talking about your political beliefs
“I support / back (the Labour Party).”
“I’m a Conservative / Liberal / Socialist / Labour Party supporter.”
“I’m a life-long (Conservative / Labour Party supporter).”
“I’ve always voted (Tory, Liberal etc).”
“He’s a staunch Conservative.”
“She’s a dyed-in-the-wool Marxist.”
Speaking tip
To avoid misunderstandings or arguments, only talk about your political or religious beliefs in conversations with people you know well. It’s probably also safer to avoid religious or political discussions with colleagues at work. The British, in particular, tend to view political and religious beliefs as extremely personal, and can sometimes find too much public discussion of these embarrassing or even insulting.
Here are some phrases you can use to “exit” an uncomfortable discussion.
“I’m not really comfortable talking about… if you don’t mind.”
“I’d rather not discuss my (political) beliefs if you don’t mind.”
“I’m not sure this is the right time / place to discuss …”