This is a practical oversimplification which will be right most of the time. For more detailed information see Mastery of the Tenses!
For routines and habits
- I go for a run every morning.
- They always go camping in France.
- I call him whenever I can.
For things that are permanent or always true
- The shop opens at 9am.
- Water boils at 100 degrees Celsius.
- I am British.
For schedules, timetables, fixed events
- The film starts at 9.
- The plane leaves at 15.30.
- The museum opens in November.
- Turn right at the lights and go straight on.
- How do I turn this on?
- First you fry the onions and then you add the spices.
For state verbs, usually.
eg agree, believe, hate, know, like, love, prefer, understand, smell, etc
- He doesn't understand the book.
- NOT He isn't understanding the book.
- I don't believe in meditation
- NOT I am not believing in meditation
For Zero Conditionals
- If the book is late, you pay a fine.
- If he says he loves you, he means it.
- If you know the answer, tell me!
For First Conditionals, IF clause
- If it rains, I will...
- If I study hard, I will...
- If she calls me, he will...
- I'll phone you when I get home.
- When you arrive, turn on the air conditioner.
After AS SOON AS when you mean ‘immediately after’.
- As soon as I hear, I will let you know.
- There'll be hell to pay as soon as he finds out!
After AFTER, the Present Perfect is also possible (with no change in meaning).
- After I speak to you, I will go home.
- After I have spoken to you, I will go home.
- After I cook dinner and I have eaten it, then I will be happy.
With BEFORE when referring to the future.
- Before the film starts, I would like to tell you that...
- Tell her you love her before she leaves you!
- Let's stay out until it gets dark.
- The cat will stay asleep until he gets hungry.