Conditionals 

Zero conditional: Used for things that are true, facts, and happen often: Both parts of the conditional are in the present tense:

If I go to McDonalds, I always get a Big Mac – I always do this When it rains, I wear my waterproof jacket – I always do this If it rains, the grass gets wet – It's a fact

First conditional: Used to talk about things that are likely to happen in the future; One part of the conditional is the present and the other is in the future, usually will is used, but we can also use might/

If it's sunny tomorrow, we'll go to the beach I won't go to the cinema if it rains

If he gets away from work earlier, then we might go to the beach

Note: A common mistake is for students to produce the sentence 'If I will go... ' this is incorrect and we should get in the habit of using the phrase 'If I go..'

Second conditional: Used for giving advice, for hypothetical, and highly unlikely situations. We can use it to talk about the present, and the future. One part of the sentence is in the past and the other part usually has would followed by a verb without to.

Note: you can not use TO after modal verbs like would/should/could/might.

If I were you, I'd go to the doctor – advice

If I won the lottery, I'd buy a house – hypothetical (future)

If you were a monkey, you could climb that tree – hypothetical (present)

Third conditional: Used to imagine how the past could have been different. The if sentence uses the past perfect, and the second carries a modal verb, usually would and have followed by the 3rd form of the verb.

If I had not downloaded Skype, I would not have opened this file – both actions happened If I hadn't cheated on my wife, she wouldn't have left me - both actions happened

If I'd seen, I'd have talked to him him – neither action happened

Note: When we use the negative form in the third conditional it means it DID happen. Also, do not be afraid to use HAD HAD, although in spoken English the first had is usually formed in a contraction 'If I'd had a 10 pound note........................................................... '

Mixed conditional: used to show how something in the past has affected the present. The if part of the sentence carries the past perfect like the 3rd conditional and the other past carries would or similar like in the 2nd.

If we hadn't won the war, we would be reading this in German.
If I hadn't asked that girl to dance, we wouldn't be married now

Note: to separate the two parts of a conditional sentence we use a , - comma. If the conditional sentence starting with IF comes in the second half, you don't need to use the comma. This of course, is only for written English.