The problem you're struggling with is one of the core issues addressed by David Allen's Getting Things Done.
Consider the to do list items
go to bank and
work on thesis. Assuming your banking task is fairly straightforward, this is a simple action. The second is a several-year endeavor. When most people look at a list like this their mind is drawn to the one that they know how to accomplish and that has a closer time horizon. Off to the bank!
GTD's advice is to abandon the to do list and replace it with a set of context lists. Most to-do lists contain an amorphous, incomplete list of things on your mind. In contrast, a context list contains actions: small, well-defined tasks that are roughly the same "size" as everything else on the list.
Perhaps more importantly, the items in a context list are defined by the context in which they become actionable. For example:
- the @home context list doesn't include filling out a work expense report that requires receipts in your office desk
- the @work list doesn't include a reminder to fold the laundry
So in your case,
Learn Spanish is a great project (GTD's name for any long-term goal that will require multiple actions to complete), but it's a crappy action. Action look like:
- "Research Spanish learning software on the internet", which could then go on an @web context list
- "See when the next Spanish I class is being offered at Valley Community College".
I find that when I'm struggling with a big "action" it's because it's not really an action but a big-ass project, and that the reason I'm struggling is either that I'm still on the fence about doing it at all or that I haven't put in the thought required to decompose my idea into actionable tasks.