The first thing I do is remove the shells off of the shrimp and set them aside, I never throw away the shells, I use them to make a shrimp stock.
Melt your butter and olive oil together until warmed through, add your garlic, I do not let this get too hot, just enough for the garlic to warm through and flavor the oil, then I remove it from the heat.
Boil your pasta, I always salt the water, during the last 5 minutes, I put the shrimp on a baking sheet sprinkled lightly with olive oil and salt and pepper and roast it for about 5 minutes or until done, it does not take long at all. By this time your pasta should be drained , pour the oil mixture over your warm pasta and put onto a platter, put the cooked shrimp on top. I serve with parmasean cheese at the table, that way everyone can add their own.