This is a super-broad question and there is enough to say about it to write entire books on.

That said, you've got a few basic tools at your disposal that, combined with some expertise in lead life cycle management, can really help you optimize your funnel and help you help your prospects help themselves.

The fundamental tools you have are messaging and your own ability to sell (even when it's a soft sell).

By getting smart about understanding the funnel, and using tools like marketing automation systems to implement lead nurturing and to start making sure that you're getting targeted content to prospects at the right time... And most importantly to make sure that you're always reminding your prospects why they signed up with you in the first place... You can seriously boost your engagement and help people get over their personal hurdles.

One of the biggest challenges in online marketing is the concept of friction vs momentum.

What you're talking about is leads who you felt had great momentum and were pushing towards the sale... What happens offline (where you can't see) is that life throws a bunch of friction at the which slows them down and they lose their momentum. When this happens the lead falls back into their routine and moves away from making a change (which is actually what you're hoping to get them to buy).

What you need to do is strategically apply some grease to your prospects to help them slide on through to the goal of changing their situation (by purchasing your course)

The good news is, the process if building this out will really help you understand your prospects, your customers, and as a byproduct your own business... Which is really cool :)