1.) Если в момент речи было решено сделать что-то и идея пришли именно тогда:
It's raining, I will take an umbrella.
I am very tired, I will have a rest in my room.
We are very busy, we will not go to the park in the evening.
2.) Когда предсказываем будущее, надеясь, что это произойдет, основываясь на фактах:
You worked hard last year. I hope that you will pass the exams well.
You have done your homework. I hope that you will get good marks tomorrow.
She learnt a poem by heart. I hope that she will answer well at her Literature lesson.
3.) Когда мы обещаем что-то сделать:
I will not have dinner without you, promise.
I will not go for a walk if I don't do my homework, promise.
I will not speak louder any more, promise.