Children don't have a lot of input in what they do or where they go. Offering them choices throughout the day gives them a sense of empowerment and independence. If they are given a lot of choices during the day they are less likely to resist the times they do not have a choice. Offer simple, benign choices such as, "Would you like to play with your blocks or your cars? Would you like to wear the blue shirt of the yellow shirt?"
Using choices as a discipline tool can be harder, but it can also be very effective. Your child may not have a choice about whether to leave the park or not, but you could give him/her the choice of how to leave the park: "Would you like to walk home or run home, or when you leave a friend's house, "Would you like to leave now or in 5 minutes?". Parents often ask children questions rather than give direct commands, for example: "Would you like to have dinner now?" We are trying to be polite, but we give them the option to say no. I assume that in most households children do not have the choice of whether to have dinner or not, but they might have the choice to decide how they will eat. "Would you like to use your blue fork or your red fork tonight?" This tactic often redirects children enough to start thinking about their choices, rather than resisting the command.
A few things to keep in mind when using choices: keep them simple and easy-to-understand, give only two choices (more than two can be overwhelming), and make sure you can live with either choice (if you give your child the option to put his shoes on or stay home, you better be ok with forgoing your plans if he chooses that option).