A black pen--or marker--and paper is all you need to start sketching. Pencils can be used too; however, since they can be erased, it may be tempting to waste time correcting non-essential details. That will only slow you down.

Making your sketches in black and white is enough. Blue and red pens for different text colors or highlighted elements can be helpful too. Similarly, a pencil or a gray marker can be useful for adding shadows or deemphasizing some elements.

You don't need to make perfectly straight lines. Making lines with a controlled and fluid motion is enough to contribute to the clarity of the sketch, but it is totally fine for lines to look hand-made. In the case you really need some guides, you can use a ruler or a business card.

You can sketch on any writing surface. Different formats can be useful, depending on the context:

• A notebook helps to keep all sketches together, which is convenient to move them around and find them later. Plain paper pages allow you to focus on the sketch, but you can also consider using a notebook with squared or ruled pages for extra guidance.
• Using separate sheets of paper provides you flexibility on the surface to use. You can fold the paper, cut it, and rearrange multiple pieces.
• Sketching on post-its note helps keep sketches in smaller spaces and makes it easy to cluster them.
• Sketching on whiteboards is useful when discussing ideas with others who may want to contribute to the sketch. In these cases, remember to take pictures of the whiteboard if you don't want some of the good ideas to get lost.

Sketching happens mostly on paper, but there are also digital tools that can help with the sketching process. When you need to share or organize your sketches digitally, you can still start the process on paper and scan or take a picture of the results.

It is also possible to directly sketch using digital tools. Graphic tablets or digital tablets allow for stylus input that simulates the interaction with paper. There are many different apps available for painting or drawing that can support the sketching process.

Digital tools can provide the unique advantages of a digital medium such as having infinite art-boards or the possibility of real-time sharing with remote collaborators. It is also possible to use digital tools to sketch on top of existing solutions using a screenshot of your current product as a background in order to communicate variations on them. However, all these additional capabilities present the risk of providing too many options and causing distraction or encouraging you to get lost in the details.