Well, for starters, Limit the use of plastic. Carry jute bags, paper bags which are easily biodegradable. try using public transportation, for avoiding excessive usage of petroleum products. Use battery run vehicles. try Not throwing your Leftover's, Products, here and there on the road.
Try keeping clean places clean! Eco-friendly travel has a lot to do with traveling responsibily.
I always make sure to carry my own refillable water bottle and not buy plastic bottles. I also do not to throw any trash in the natural environment - not even a small chocolate wrapper in the places I visit. I always carry it back and dispose it in eco-friendly way.