There are actually two different forms of "to think" at work here, and they're not interchangeable.
You can say that you are considering something or something is on your mind by saying "I think of/about (something)". Here, (something) is an indirect object (and thus must be a noun), it's a thing you are thinking about:
She thinks about business.
I'm thinking of dinner.
Alternately, you can say that you have an opinion or position about some subject by saying "I think that (something)". Here (something) is a clause expressing some specific idea or position you have. That is, it is essentially a sentence of its own, which is included in the larger sentence using "that".
She thinks that business is important.
I'm thinking that dinner is going to be late tonight.
Now, there is a common idiomatic tendency with verbs like this that express opinions ("to think", "to feel", "to say", etc) to simply leave out the "that", so quite often people will say the following instead (which means the same as above):
She thinks business is important.
I'm thinking dinner is going to be late tonight.
When there's no preposition there, it's always an implied "that" (never "of"/"about"), and it always needs a full statement after it (not just a noun), so the following are wrong:
She thinks business. (wrong)
I'm thinking dinner. (wrong)
Now, in your example sentence, that's what's happened (they've dropped the "that"), but they've also gone one step further. When you're expressing the idea/opinion that something is something else (i.e. "I think A is B"), there is a (less common, and rather stylistic) option of also leaving out the verb "is" from the clause, like so:
She thinks business important.
I think the movie pretty interesting.
Note that this can only be done when the verb is the simple present tense "is", not other forms of "to be", so for example, the following does not work (because the full verb above is "is going to be", not just "is"):
I'm thinking dinner going to be late tonight. (wrong)
Actually, saying things this way is pretty unusual, and can often sound a bit strange, so it's not generally something I'd recommend people trying unless they're really familiar with it. It does have something of an antique feel to it so it is often done when somebody is trying to be fancy with their language. However, a different verb that you can do this with, which actually is more commonly done and is less likely to sound strange, is "find", as in to come to have an opinion about something:
She finds business important.
I find the movie pretty interesting.
(These don't sound that unusual)
Another form you may come across is to drop "that" and replace the "is" with "to be", which also means the same thing:
She thinks business to be important.
I find the movie to be pretty interesting.
Note that in all of these cases, however, we're using "think"/"feel"/etc to express an opinion about something ("business is important" or "the movie is interesting", etc), as opposed to actually thinking about something, which is a different sort of action.