First Steps Edit
People are worried about starting and getting accepted at the Big 3. Don't, sit back and relax. If you don't know where to begin, get a spreadsheet going and enter in the required courses. Find all required courses from what's available and plug in that info. Work on those courses.
Your first step should be to find the degree and requirements for that degree and create a spreadsheet. Second step is to work on most of those requirements, I would get almost halfway, such as getting all your Gen Ed + Free Electives done. Third, apply to ACE Credit Registry and have your courses sent to them if they are ACE recommended. Four, apply to Big 3 and send them your transcripts from ACE and whatever else you have. Five, speak with an adviser on completing your AOS (Area of Study) courses and match it with your spreadsheet.
Basically, you might want to plan and map out your degree, fill all those credits up, and apply at the latest point. The reason is you will have all your stuff together for them to process and graduate before they charge you another annual enrollment fee. This is explained on the wiki actually. Please take a bit of time and read the DegreeForum wikia page, it helped me and others as well.
If you're still confused, the Big 3 allows you to transfer pretty much everything but their capstone and cornerstone courses. This means, you don't need to apply right away. You can spend 6-10 months, get 90+ credits or more and then apply to them. Note: You don't have to send them anything until you are ready, example, transcripts. Don't rush yourself and work your courses according to your own plan and pace.
Which courses to take first, when to create an ACE Credit Registry account? Checklist Q&A: I usually tell people to begin with the FREE courses first as it will give you an idea of online learning. If you complete the free gen ed elective/free elective courses, there's no cost for easy credits to start you off! See Free Sources of Credit.
Start your ALEKS College Algebra, it's $20/month, if you can finish quickly do the Intro to Stats. These two are the most recommended courses, if you want more, you can go for Intermediate Algebra and PreCalc. For me, I am taking all 8 for a max of 12-18 credits total, it depends on the school accepting the credits. Guess what? You're at 23+ credits, it cost you just $20-$40, and you are pumped up to do more cheap courses! When you are done all of these, continue updating your spreadsheet and you can then start your Saylor or Straighterline courses.
What's the easiest method to go through the FREE credits quickly? It's not proctored! It's an open book exam. So, open multiple browsers/tabs (or a second monitor) and go through them. Especially when you have the free NFA, TEEX courses, you can have the answers at your fingertips. Have the questions on one screen/window and have the course materials open on another tab/window.
For ALEKS, I go through topics and it's the online calculators that I use to "confirm" my answer is correct. In order to check steps to get to your answer (explain hyperlink), I also have the Master Account open to view previous assessment. I do an assessment, go through topics until I reach a few % higher (or to 70%), and do another assessment. You need to do this a few times until you reach the 70% or higher on the last assessment; once there, request your ACE credit.