Getting Things Done recommends identifying the very next action ("NA") in your projects.
The next action is actually a physical action. For example, if the next thing you need to do is talk with Jan about something, then your next action is "find the address book, look up Jan."
The idea (as described in GTD) is that by focusing on only the very next action, we make the task more palatable to our mind. "I don't know that I have time and will to do my taxes, but I do have the time and energy to find the address book."
After you have the address book in hand, it's a short step to looking up Jan, and once you're staring at her phone number, it's just a matter of course to dialing Jan. When she says, "Hello?", what naturally follows is what you meant to call her about.
But don't worry your head with all those details; You just focus on getting the address book. And that's all you put on your next actions list: "Find address book, Jan's phone number."
The Next Action should always be an actual physical action. Pick up the paper and read an article, look up the number to the vet, find the duster, fetch the report. Avoid vague (and cumbersome sounding!) items like: "Complete the Project, Deal with Fluffy, Clean the House, Clear off the Desk." See all those capital letters in there? That's what it feels like, to your mind.
To make your Next Actions (and Projects incidentally) look and feel actionable, use verbs to start the name of each one. For example: Take Fluffy to the vet, File old bills, Mail Bob's birthday card. For inspiration, take a look at the Next Action and Project verbs from David Allen's original Getting Things Done Fast CD booklet.