To me - think of means to think of an example. Think about means to think about different aspects of a thing. So - you would 'think of a number between 1 and 10'. You would think of words that might fit in a crosswords. But if you thought about the sea, you would think of the colour, the smell, the taste, the way it moves...

Make an example of these two phrase based on my understanding. Every time I couldn't put up with Bob anymore, I would think of a divorce. (means I got an idea of divorce). Yet if I think about divorce, meaning I would evaluate how much price I shall pay for a divorce, consider how about the child custody, financial problems, etc, that consequent situations by a divorce.

Think of = opinion Think about = process or detailed opinion

'Thinking of' usually means 'considering'. 'I'm thinking of a new car' would mean considering replacing your current model, whereas 'thinking about a new car' is what you do when watching the adverts, without necessarily planning to buy one. (So 'thinking about getting a new keyboard' would involve "Well, typing would be faster, but it's another cable to tangle, and it costs a bit, and..."). But it's only a connotation, not a meaning, and don't try to apply it to your sweetheart!