1. Conditionals

2. Simple present if simple present
Conditional: type 0
Used to talk about facts that are ALWAYS true.
If simple present, simple present
Simple present if simple present
If I eat too much, I get sick.
Ice melts if you heat it.

3. Conditional: type 1
Used to talk about a possible present or future situation and its result.
If present tense (simple or cont), any form of future
(going to, will, can, could, may…)
They won’t get a table unless they’ve already booked.
Can I borrow your pen a second if you’re not using it?
If it stops raining, I’m going to walk into town.

4. Conditional: type 2
Used to talk about hypothetical or improbable situations in the present or future. Also to give advice.
If + past (simple or continuous), would + verb
(could, might)
If I were president, I would cut taxes.
If I lived in Canada, I would speak English fluently.
If we had a bit more time here, we could go on an all-day river trip.

5. Conditional: type 3
Used to talk about a hypothetical situation in the past.
If + past perfect (S or C), would have + p. participle
(could have, might have)
I would have picked you up if I had known what time your flight arrived.
If I’d been looking where I was going, I would’ve seen the hole in the road.

6. Alternatives to IF as long as / so long as
I’ll tell you what happened as long as/so long as you promise not to tell anyone else.
provided / providing (that)
Provided/Providing (that) the bank lends us all the money we need, we’re going to buy that flat we liked.
on condition (that)  formal
They agreed to lend us the car on condition (that) we returned it by the weekend.
unless  meaning if not (only first and second conditional)
You won’t get the job unless you improve your English.
otherwise  meaning if not
You need to improve your English. Otherwise, you won’t get the job.

7. Alternatives to IF whether + subject + verb + or not
I am not sure whether you are telling the truth or not.
I am selling my car whether or not you like it.
even if for extra emphasis
Even if I get the job, I would not rent a flat.
Supposing
Supposing Internet hadn’t been invented, how would that affect your life?
If it wasn’t/weren’t for or If it hadn’t been for + noun to replace an if clause.
If it weren’t for her dog, she would be very lonely.
but for to replace if it wasn’t/weren’t/hadn’t been for.
But for her dog, she would be very lonely.

8. MIXED CONDITIONALS
When we talk about mixed conditionals, we are referring to conditional sentences that combine two different types of conditional patterns. These combinations are not all that frequent, but the most common combination is when we have a type 3 conditional in the if-clause (if + past perfect) followed by a type 2 conditional (would + infinitive) in the main clause.
mixed third / second conditional 
With this combination we are contrasting an imagined or real event in the past with the present result of that. Consider these examples: 
If he'd taken the medication, he wouldn't still be lying sick in bed. 
If she'd taken reasonable precautions, she wouldn't be pregnant now. 
If he hadn't run after the car thief and suffered a heart attack, he'd probably be alive today.

9. MIXED CONDITIONALS
mixed second / third conditional 
The other possibility, though I think this is less common, is when we have a type 2 conditional in the if-clause (if + past simple) followed by a type 3 conditional (would've + past participle) in the main clause. 
With this combination, we are describing ongoing circumstances in relation to a previous past event. Consider these examples: 
If you weren't such a poor dancer, you would've got a job in the chorus line in that musical. 

10. INVERTED CONDITIONALS
We can use the inversion with the following conditional forms. It is more formal.
Should you have any question, feel free to ask.
Were he to find out the truth, he would be heartbroken.
Had they suspected the man, they would have turned him in.
Had we not acted, the consequences might have been even worse.

11. IF + GOING TO To express an intention:
If you are going to have a party, you should warn your neighbours first.
A result that is obvious from a present situation:
If it’s going to rain, you will need your umbrella.

12. IF + MODALS
Politeness
If you would like to follow me, I would take you to the meeting room.
Willingness
If she will accept the deal, the company would benefit.
Unwillingness
If she won’t change her behaviour, we will have to take action.
Anger
If you would just listen to me, you might understand what I’m saying!