There's a lot of answers that go to your question, i.e., your question is only scratching the surface. I'll start with a very high-level answer that I hope puts you on a path of generating a ton more questions.
An action plan begins with the definition of finish. You literally work backwards from finish, right to left instead of left to right. If you are having trouble visioning what your next steps are, it is likely due to the fact you do not have a clear vision of what finish looks like. So that's step 1.
The next step is to break down your definition of finish. This is called a Work Breakdown Structure (WBS) where you take your finished product and "break it down" into smaller, more manageable products. Once your product is broken down to the degree you think is appropriate, you can then identify the tasks required to build that product.
Next is estimating the work (in hours) and duration (in days) for each of your identified tasks. There's a lot that goes into this and needs to include those who will be doing the work. This should generate a lot of questions.
Next is sequencing. There are three types of reasons you would logically put one set of tasks before the next. First is due to a logical sequence due to the nature of the work, e.g., you cannot paint the wall until after you finish hanging the drywall, taping it, sanding it, etc. Second is due to the availability of resources, including people, to do the work. If you have the same person doing task a and task b, she can only do one at a time so one of those tasks will be sequenced after the other. And third is by choice; you simply schedule one task after the other.
Now you can put all of this against a timeline and dates and times. Literally, because you have already established the logic, you identify the start date and the rest of the dates and times will simply flow from there.
This is a very high-level answer to a complex activity and is considered to be a waterfall type approach. There are other approaches, such as Agile, that you could take advantage of, too, and perhaps someone can provide an answer using that method.