If its a new product that has never been seen before or a copy of an old product, a customer will eventually use the thing. Even if it is just for your personal use, write down your needs so you can hit all your goals.
For this project I wrote down what I wanted in a desk.
Movable, clean, designated storage, expandable (plenty of room on desk surface), durable, clean European design, not white, plenty of leg room, always organized, standing desk with ability to sit down.
if you actually interview a customer then observing them using a similar product or several products is the best way to understand how it can be improved. In addition to comments they make watch for minor issues they have and write them down.
Also this website is a great place to look for feedback, as most likely there is someone who has a similar project and has some suggestions of how it could be improved.
Next its time to simplify the comments and notes in to specific actionable solution independent items. For instance movable is not an easily quantified action so I will split it up in to if it can fit in to my car as a pas fail test and weight . the reason this is important is we are trying to take the burden of managing all the requirements and simplifying them where we can. Also some requirements are going to be more important as we will see later.
Movable => lightweight + fits in car
Clean => this is an aesthetic which is up to the designer however copying good design can help with this part.
Designated storage => organized
Expandable => variable working surface area
Durable => Tough (Mechanical engineering definition)
not white => low light reflection
leg room => open area beneath desk
standing desk with ability to sit down => adjustable working surface height