Ten phrases in the local language — please, thank you, hello, goodbye, excuse me, how much, where is, water, restaurant, help — transform travel interactions. Locals respond differently to travellers who've made any effort. Most travellers know zero; the small preparation matters.
How to learn
Phone app (Duolingo, Memrise, Pimsleur). Phrase book the night before arrival. Practice on first day until basic phrases are automatic. Doesn't take more than 1-2 hours total.
Most travellers report this as the highest-leverage 1-hour pre-trip preparation. Costs nothing; produces noticeably different travel experience.