Page 456 - Practical English Usage 3ed - Michael Swan, Oxford

5 if, as if and as though
It is used to introduce some clauses with if, as ifand as though. It looks as ifwe're going to have trouble with Ann again.
It's not as if this was the first time she's been difficult.
It will be a pity if we have to ask her to leave.
But it looks as though we may have to.
6 It was my aunt who took Peter to London
It can be used in 'cleft sentences' (see 131) with who- and that-clauses to emphasise one part of a sentence.
It was my aunt who took Peter to London yesterday, not my mother. (emphasising my aunt)
It was Peter that my aunt took to London yesterday, not Lucy. (emphasising Peter)
7 It's amazing the way they work together
It is not normally used as a preparatory subject for noun phrases.
The new concert hall is wonderful. (NOT It's W6rttierfttl the new ooneeFt MH.) Butinaninformalstyle, itcanbeapreparatorysubjectfornoun+relativeclause.
It's wonderful the enthusiasm that the children show. This is very common with the way . ..
It's amazing the way (that) they work together. It's strange the way you know what I'm thinking.
For passive structures with it as a preparatory subject. see 417.
447 preparatory it (2): object 1 I find it difficult to talk to you.
We can sometimes use it as a preparatory object. This happens when the object of a verb is an infinitive expression or a clause, and when this has an adjective or noun complement. For example, instead of saying 'I find to talk to you difficult', we prefer 'I find it difficult to talk to you'.
subject + verb + it + complement + infinitive/clause
We found it tiring to listen to him.
My blister made it a problem to walk.
1 thought it strange that she hadn't written. George made it clear what he wanted.
Note that this structure is not normally used when there is no adjective or noun complement after the verb.
1 cannot bear to see people crying. (NOT I etltlrtt'Jt beal' it tt'J see poople eryillg.)
1 remember that we were very happy. (NOT I I'emef7zbel' it that . ..) But note the structure 1 like/love/hate it when . ..
1 love it when you sing.
Note also the idiom 1 take it that ... (= I assume that ...).
1 take it that you won't be working tomorrow.
preparatory it (2): object 447
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