Although I've already written about most commonly used phrases to express opinions in English, at different levels of formality, I was so happy to come across this IELTS video lecture while preparing for my online lesson. I'm sure you'll enjoy watching it and learning from it as well:

When preparing for an IELTS test, it is more important to expand your functional vocabulary, rather than the topic vocabulary. The reason is very simple. For example, OPINION PHRASES will be needed both in the first and second and third part of the speaking text. Therefore, you can use opinion expressions, both for strong opinions and weak opinions.

English Phrases in Situations

• General phrases
• Saying hello
• Saying goodbye
• Phone conversation
• At the bank
• At the supermarket
• At the market
• At the chemist's
• At the hotel
• At the restaurant
• At the cafe or bar
• At the post office
• At the travel agency
• At the doctor's
• At the dentist's