According to the English Grammar in Use (Second Edition) in general we use SOME in positive sentences and ANY in negative sentences and most questions:

• (+) We bought some flowers.
• (-) We didn’t buy any flowers.
• (?) Did we buy any flowers?

ANY

We use ANY in negative sentences or when the meaning of the sentence is negative:

She went out without any money.
He refused to eat anything.

In these cases the word is preceded by oder words that have a negative meaning, such as the preposition without or frequency adverbs that are used to refer to things that almost never happen or do not happen very often, such as: hardly, rarely, scarcely and seldom.

ANY is also used in most questions:

Have you got any luggage?
Has anybody seen my bag?

We often use ANY after if:

If there are any letters for me, can you send them on to this address?
Let me know if you need anything.

Or when the sentence have the idea of if:

I’ m sorry for any trouble I’ve caused.
(If I have caused any trouble)

We also use ANY with the meaning “it doesn’t matter which”

You can catch any bus. They all go to the centre.
(it doesn’t matter which bus your catch)

SOME

SOME is used in positive sentences but, despite in most questions we use ANY, we should use SOME in questions when we expect the answer to be “yes”:

What is wrong? Have you got something in your eye?
(It seems that you have got something in your eye so I expect the answers to be yes.)

We also use SOME in questions when we are offering or asking for things:

Would you like something to eat? (offer)
Can I have some sugar, please? (ask)

Or we can also use SOME to talk about a person/thing that we know/think exists.

Are you waiting for somebody?

SOME: positive sentences, questions (talk about a person or a think we knows or think exists; to offer or ask for things; when we expect the answer to be yes).

ANY: negative sentences, negative meaning, most questions, after if, when the sentence have the idea of if, with the meaning “it doesn’t matter which”.