Structure of first conditional

Structure of the first conditional
positive negative question
If I see him, I'll (I will) tell him.   If you don't hurry, you'll miss the bus. What will you do if there is a problem?

The first conditional - common mistakes
Common mistakes Correct version Why?
If you will go to England, you will improve your English. If you go to England, you will improve your English. We use the present simple in the if-clause.
If I find his address, I send him the letter. If I find his address, I will send him the letter. We use will in the main clause, to express certainty in the future.
I'll tell him if I will see him. I'll tell him if I see him. We use the present simple in the if-clause.