If it's a gift: choose a teddy or a stretch lace set. Stretch lace and one piece styles forgive a guessed size far more than a corset or an underwire bra.
If you want it to photograph well: go warm and bright. Cherry and scarlet hold their color under a flash. Deep wine shades can go muddy in low light.
If you want structure: a steel boned corset is worth the fitting effort. Corsets are sized by natural waist, not by letter, so measure your waist and check it against the size chart.
If you want an easy win: add red panties to lingerie you already love. A red crotchless or pearl style changes the whole look for the price of one piece.
If it's for Valentine's Day or Christmas: order well ahead of the date. Holiday shipping runs slower than the rest of the year.