My number one tip is to challenge yourself, call random hotels and ask if they have certain things there (ie "do you have a spa/swimming pool") or stores and ask them what their closing hours are. The main idea is to focus on sounds that you struggle with most (example: asking if a hotel has a sauna and steam room if the sound you struggle most with is "S"). Stuttering on purpose while doing this is a fun thing to do also, as it challenges your brain to face the reactions and 9 times out of 10 they aren't a big deal. The more you push out your comfort zone, in my experience, the easier it gets.