用英语表达“建议让他开心起来”可以有多种方式，以下是一些常见的表达：
- Suggest making him happy.
- I suggest making him feel better.
- It would be a good idea to cheer him up.
- I recommend trying to lift his spirits.
- You might want to consider doing something to make him happy.
- I propose finding a way to brighten his day.
- It’s a good idea to think of ways to make him smile.
- I advise doing something to bring a bit of joy to him.
- You could try to make him happy with a small gesture.
- I suggest finding something that would make him cheerful.