To create an 'ideal' defense garrison you need to predict as accurately as possible what sort of invasion you'll be faced with.
For example, if you have a land locked country and you know it will be land locked for a very long time, then you should place more emphasis on air defense and less on land defense.
The default garrison blueprint is a very well rounded set up, placing defense against land and air/naval invasions.
Just remember that only a few targets can be nuked so you won't need nuclear defense batteries on garrison blueprints for such things as forts and counties.
It is wise to use the maximum 2001 weapons to defend such targets as your capitol, airports, and bases. For smaller and less targeted targets you may decide to use a smaller blueprint with the minimum amounts of weapons.
For such blueprints as the capital, bases, and airports, I suggest placing some extra nuclear defense batteries on these, just sub