I've been looking for a way to get around the lack of sub tasks and dependent tasks in RTM so that I can apply next actions (na) and so far, the suggestions that I have come across have not been working well for me.

I've finally come up with my own system which has proven useful and I want to share:

I set a list for each project that I am undertaking and for each group of tasks, I put a bullet point before the task name so it look like this:

a. task 1
a. task 2
a. task 3
b. task 4
b. task 5
c. task 6

Note that the letters do not signify the order of importance, I have priorities for that. This way, once I complete a task in a set of bullet points, I can easily see what other tasks are part of that group (dependent tasks) and then assign a next action (na) for it. If I think of a new task that is dependent, I can quickly add it to the group without any hassle.

I only do this for tasks that are group/dependent in a project. If the project has tasks that are not dependent, I just enter the task without any bullets and they go to the bottom, which makes it easier for me too.

The only issue I have run into this so far is if you have tasks that start with the same letter as a bullet. For example, if you have bullet c and you have a task Check Bill, it will populate after the tasks in bullet. This can be an issue if you have bullet d. In such a situation, you can group all single tasks as bullet z :)

I have seen other systems that take this even further but I wanted to keep my simple straightforward and flexible and this seems to be the best option for me.