I use Contexts as "category/location" similarly to GTD but not very effectively...I need to rework my Context system sometime -- right now it seems all of my tasks are in "@Computer", @Home, and @Phone Calls -- which doesn't narrow the field much, because honestly, 90% of the time I am at home, next to my laptop, with a phone next to me -- so I would like other people's input on that.
So to narrow my priorities, I've been using Goal plus Starred. Starred is my "working list", and Goals are the things I look through in the morning to create the Starred list.
As for Projects...Let me back up a second and work up from the bottom. GTD (Getting Things Done, which I draw from) has a concept of a project (lowercase P) which is a collection of actions. At first I tried to make all of these have the MLO Project attribute set (isProject=true). But what I found is that it wasn't helpful for me, and I didn't need it -- instead, if I broke down each item into actions and used the parent as both the container and the last, wrapping up step, it works well. So ideally I try to make my initial entry be descriptive of the whole task: "put in a new garden". When I'm ready to think about it, I break it down -- "put in soil", "build retaining wall". Each of those is sometimes broken down -- "call landscaping company to arrange rock delivery". (To be truthful, they are often broken down only in my head, which is not the most effective, but is reality). This then "bubbles up" on my task list, first "call landscaping", then when that is finished, "build retaining wall", then "put in new garden" shows up when all else is complete, and it reminds me to tie up any loose ends. So once the children are complete the container becomes another leaf task, basically.
Another thing you need to know to understand this system is that my tree is organized by Area of Focus -- AOFs, e.g., Self, Life Maintenance, Career, Family. These are the tops of my tree, everything goes under one of them.
So I thought about what I wanted to use the Project attribute for, mainly based on what views on Android use it, because I can customize the desktop but not Android views. On Android there is a Projects view and Active actions by Project view. So I decided to use it to show me a list of all my "big rocks", the things I want to focus on. My bigger picture.
So I made all of my AOFs be Projects, as well as whatever sub-projects/goals I want to have in this big picture view. E.g., I'm planning a writing retreat for a group of mine. It lives under "Self". So in my Active by Project list, I have both "Self" (which has all the random tasks under it in that category) as well as "Plan writing retreat" right under Self (ie, in the right order because the order is tree based).
Now, when I start thinking about it (which ideally would happen in a weekly review), I'll change it's Goal status to whatever horizon of focus I want, so that it appears in my sorted list of active actions when I'm looking through to select my daily tasks.
I hope that helps...my system is always a work in progress, and it's in no way perfect...in fact it's probably time to tweak it again so I use it more effectively.
Lisa