I have to quibble with this. It's a common misconception that a project "should" only have one next action. It's late and I don't have the energy to find the page in the book that discusses this, but DA actually recommends that if you have multiple next actions you could be working on in parallel for a project -- because they are not dependent on something else happening first -- you list them all in your next actions lists. If a possible action is something you can't act on now, you can park it in project support.
Since the majority of projects tend to be simple enough to have only one next action at a time, I don't think there is a lot of danger in overloading your NA lists by including all of the immediately actionable steps for those few projects that will be more complex.
I see that I may have been a bit "strict" in my wording here, using the word "only". Let't put that on the "not being a native English speaker" account...
The only "set rule" when it comes to projects, is to have
at least one next action for every project, in order to make meaningful progress towards completion - keeping in mind that a project has a time frame of 12 to 18 months, hence the need for reviewing weekly.
I have encountered quite a lot of people in my courses that feel the need to "think through" their projects, with potential overload as a result. You (
@bcmyers2112) and I have the "GTD mind set", but for someone starting out, the concept of doing just enough thinking to get stuff off of your mind can seem a bit radical.
I follow you when it comes to next actions in parallel projects. I don't think I have any parallel projects at the moment, but for me, this has the most value if the parallel actions reside in different contexts. If all actions are to be executed on a computer, for example, I prefer having only one at a time as if it was a serial project - again, not to overload my list. This of course depends on the number of projects you have. At the moment I have 41 active projects.
Also, I was talking about actions that are allocated to the different context lists. I have heard in several GTD podcasts and also from different coaches that the recommended practice is to rather store future actions either in the notes field of your project list or in a separate project note, for later "activation". By flushing out a number of next actions for a project, you also run the risk of either not identifying ALL next actions (missing one or more), or that the nature of the project changes over time. Just a couple of days ago, I had to replace a next action in a project with another, because I was given new information...
So: Nothing wrong with having more than one next action for a project, but beware of the potential pitfalls! Personally, the value of GTD for me is more "relaxed, focused control" than "get as much done as fast as you possibly can". A possible way to deal with the issue in question, is also making a habit of revisiting your project list every time you complete an action tied to a project. Speaking of "rules", there is no one saying that reviewing you project lists only happens during the weekly review; this is just a safety net for making sure that you review it at least once a week!