I mostly avoid carrying my chapattis in a foil, if some water cannot be used i drain it into soil rather than a drain, I DO NOT throw plastic even if i have to stuff it in my bag, I refrain from chewing gums and Styrofoam cups, i take my own cup when i visit the nearby tea shop. I know of people who choose not to consume any products sold in plastic at all - so no chip, biscuits, or chocolates which are sold in plastic packs! I cannot and so do not do that, but between the choice of a bakery and a packaged item i will choose the bakery. A leaf bowl over a plastic bowl, hand over plastic spoon and so on.
Small things, 2-3 a day... but they make me feel good.
And of course i look at, touch and smell trees - when you do that, doing something for them in turn becomes really easy - its like you're doing it for a friend, most naturally.