Now that you've tried on the dress and see areas you want taken in, it's time to take it to your local seamstress- and Don't forget to bring the shoes you're intending to wear! It's important to know what shoes you intend to wear before making any hem in the dress, as depending on the height of the shoe this may change how long or short you want to have your dress hemmed. A seamstress will also help you alter the strap length and any additional modifications such as taking in the waist if you're after a more fitted look.
Pro Tip: During a busy season a seamstress may need two or even three weeks depending on how much work needs to be done to the dress, so be sure to allot for this amount of time before your event day.