Excellent question! We use a tactic here when performing very granular account optimizations that utilizes negative keywords to “force” Google to use the long tail variations of our keywords.

First, to answer your question – you could simply place [blue shoes] in the second ad group and move on with your life. However, to maximize your keyword exposure, I would recommend the following:

1. Use broad match in both.
2. In the “shoes” ad group, ad -[blue shoes] as a negative exact match.
3. In the “blue shoes” ad group, ad -[shoes] as a negative exact match.

Like I said above, this forces Google to use the long tail version of your keyword while allowing you to be open to potentially relevant broad matched search queries!

I have a question following your example with a “shoes” campaign with 2 ad groups :
1 – shoes
2 – blue shoes

In ad group 2, would you recommand to buy the keyword
blue shoes (broad match) ?
Or is it better to bid only on “blue shoes” and [blue shoes], because there is already a bid on shoes (broad match) in ad group 1 ?

Thanks for the comment. I am definitely a fan of the “easier” factor in finding opportunities for improving my accounts.

Couldn’t agree more.

Just because you may have set budget/targeting options doesn’t mean all Ad Groups belong in 1 Campaign. Makes it much easier to look for opportunities to improve/”optimize” when information is more detailed and specific.

Great post!