Do as much research as you can - the more you know about a country and its people before you arrive, the quicker you get under the skin of a place.
Learn a few words of the local language and make sure you know what's considered polite and what's not in terms of eating, greeting and dressing.
Try to leave as much excess packaging at home (eg film boxes, anything plastic) - so your hosts don't have to deal with your garbage.
Consider your transport options: could you ride a bike rather than drive? Take a train rather than fly?
Culture Shock vs Cultural Connection
One of the best things about travelling is making connections with people from different cultures, in an authentic and mutually enjoyable way.
'Cultural sensitivity' is simply a matter of respect: take your behavioural cues from the locals and, if in doubt, try to see things from the locals' point of view.
Go with the flow. Other cultures have very different concepts of time, personal space and socially acceptable behaviour. You'll find it a lot less stressful - and a lot more enlightening - if you just chill out. You might even reassess your own ideas.
Dress appropriately. Looking at the locals is a good way to gauge what to wear. Particularly in conservative cultures, don't flaunt your flesh and try to be neat and clean - it's only respectful.
Try to be conservative with resources such as water, food and energy - you may be depriving local people or making a negative impact on their environs.
Buying locally made crafts and curios means your money goes directly to the community.
Enjoy the ancient art of bargaining: part pas-de-deux, part drama, part chess-game, bargaining is a skill and an art form. It's as much about the social interaction as the final outcome. Make sure you know when bargaining is appropriate - and when it's not. Have fun with it and keep things in perspective - does haggling over that last dollar really make a difference to you, compared to the vendor?
It's when you make those cross-cultural connections - even though initially you may have thought you had nothing in common - that it hits you again: people are the same wherever they're from; we all have the same needs and desires, aspirations and affections. Ravelling in that realization is the holy grail of travelling.