This is something a lot of people on the internet are confused about, so let's make it clear. If this is a pet peeve of yours, just direct people here and we'll both profit.
Where to put spaces: The ultimate guide
Commas, put a space after them, but not before.
The same goes for: colons; semicolons. And periods. Pretty simple, right? Also question marks and anything used in place of the period. Even interrobangs‽ Sure.
It's never a good idea to put spaces around apostrophes.
Something is left - dashes. Spaces around them. But not hyphens - write e-mail together (or don't use the hyphen at all).
As Socrates said, "Quotes are confusing. But I suppose they should be used like this." (I'm not sure whether to put a second period there, so I'm adding some extra text to make you forget this happened).
Brackets (like these) should have spaces around them, but NOT inside.
Do NOT do any of this:
Lorem ipsum( dolor )sit amet.
The spaces (the ones here )are wrong.
An especially annoying type ( used almost everywhere ) ; it's a real eyesore.
One last thing before we finish (this happens a lot with brackets and commas or colons): When two rules collide (space around brackets vs. don't use spaces before commas), the rule of thumb is to NOT use the space.
Okay, one more thing (since you're already here). Please, for the sake of all beings that can read, do not use its and it's interchangeably. Its indicates possession, similar to my, your, his, her, our or their. Notice there are no apostrophes in these, ever. It's means "it is". You're means "you are". They're means "they are". Thier doesn't mean anything. There means "at the place I point to". Thank you.
And that's about it! If you use whitespace correctly, you seem twice as smart as before. Seriously - doing this wrong is unnecessary. After all, there aren't that many rules. And you won't have the grammar police complaining - so it saves everybody's time.