I've seen a couple of different approaches on this, but basically the title of your project should define your successful outcome enough to remind you of your commitment. I've also seen others define their projects as an outcome in past tense, and that works well, too. For example
"Get new tires on my car" vs
"New tires are installed on my car"
Either one of these items on your project list should remind you of the outcome to which you've committed--you need to get new tires on your car. Don't feel that you have to choose one or the other; choose the one that makes most sense for you for each project you define.
Some of the more complex projects have a number of success criteria before you can consider them finished, and it's not always possible to "capture" that information in the title of the project. For those, I suggest that you define the project as best you can with a simple title, put it on your Projects list, then make a checklist of success criteria and add it to your project support material. Review this list regularly (at least during your weekly review) to help you evaluate the status of the project and define appropriate next actions.
If you use a electronic system (Palm Desktop, Outlook, etc) where there's a freeform text "Notes" field attached to a "Task" that represents a project, I suggest you put this checklist inside that "Notes" field.
If you use a paper based system, I suggest you create a project support folder for that project, write down the success criteria checklist on a separate sheet of paper, and put that checklist in your project support folder. I suggest that you keep paper-based project support materials in a vertical file sorter on your desktop or in your general reference filing system.
I have one final thought to share. Not every project is going to have a folder full of support materials. Only create one if you need it. Don't overwork the system or try to run it too "perfectly" or it will become a burden rather than a help and you'll stop using it.
I hope that helps. Best of luck!