Every good experiment begins with a clearly defined learning goal.
When you are clear on what is it you wish to learn, then you can start chipping away at it, reducing it into smaller—more feasible and viable—chunks.
For example, one of the teams I've been working with for the last several weeks had the following learning goal:
We want to learn if the customer will care about this enough to switch their supplier.
It's a great learning goal; crisp, concise, and solid base for formulating assumptions and hypotheses.
They had to run several Lean experiments in order to collect enough trustworthy insight to reach a conclusion.
Whenever they got stuck on how to proceed, they'd just go back to their original goal—and get right back on track.
Spend some time to clarify your learning goal, and it'll save you time and frustration down the road.
If you feel stuck, feel free to dig into my step-by-step guide: