A couple of thoughts from one who has done a few boils
Cut the garlic head in half and cook. Serve the garlic do not mush it
Taste the water for the right level of salt. Too much is bad
Taste the water for pepper. Too much is bad
Using a strong burner, bring seasoned water to a boil, add shrimp bringing it back to a boil shrimp will float. Three minutes later turn off burner and add some ice to pot. Shrimp should sink as it soaks up seasoned water. Remove from pot within 4 minutes. Purpose is to avoid overcooking while still absorbing the flavors.
I do not use meat product such as sausage as it makes the product somewhat greasy as you peal.
Red potatoes, corn on cob, onions and whole mushroom are great additions
I usually figure on 3/4 lb of tails per person
Garlic bread is a great add
The beer must be very cold
Adieu