TYPE 0 (a general truth, a law of nature, sth. that is always true)

if/when + present simple /// present simple

If you mix black and white, you get grey.

TYPE 1 (a real or very probable situation in the present or future)

if + present simple /// future simple

                               /// can/must/may + bare infinitive

                               /// imperative

If I have time, I'll go to the gym.

If you finish your homework, you can go to the park.

If you go out, lock the door. 

TYPE 2 (an imaginary situation in the present or future)

if + past simple/continuous /// would/could/might + bare infinitive

If the weather was better, we could eat outside.

If she was working closer to home, she wouldn't have to take the bus.

If I were you, I would look for a new job. (giving advice) 

TYPE 3 (an imaginary situation in the past)

if + past perfect simple/cont. /// would/could/might + have+ past part.

If I had woken up earlier, I would have got to work on time.

If you had told me you were going to the party, I would have come with you. (regret or criticism)