Every now and then you're reminded of something so critical to your customers' experience that you can't believe you ever forgot about it.
In my case, I was doing some work for my carsharing client, Flexicar. I was checking out some new potential parks in a parking garage and reviewing the signage of a competitor. So, never having been to this car park, I had to use the tools our customers have available to them - in this case, our website & the map of parks...and I discovered that the publicly available information was NOT ENOUGH to find the park. The floor and bay number were NOT available. We did send more detailed information in a booking confirmation email, but what if they didn't have that with them...customers rarely doing exactly what you ask!
So by putting myself in the customer's shoes I inadvertently identified a pretty big issue - by updating the information on the site, it will ensure a smoother experience for new customers visiting that site, will cut customer service phone calls and will generally create a more positive experience for the customer. And it's the ultimate zero budget marketing fix - it will cost NOTHING to do and take only a few minutes of my time.
I have been preaching "put yourself in your customers shoes" forever - but this proves it something you need to do in ALL facets of your business, over and over again. I find that with many online businesses I visit, it's IMMEDIATELY apparent there are obvious - and quick - improvements that could be made to improve a customer experience, and improve sales.
So if it's been a while since you took a step back and tried to BE your customer, then I can only recommend giving it a go today. OR even better, sit behind someone who hasn't used your site and watch their experience with your online business (or physical space). I guarantee you'll identify several things you didn't even think were issues.