Have work to show
Develop your projects further
It is ok (and encouraged!) to expand on the projects you do in school. Consider using what you did for your class as an outline, and work through your favorite project again in your personal time, armed with all the knowledge of what went well and what didn't the first time.
Make something new
When you start working on projects for your portfolio (or even just for yourself), think about if you would rather invest your time in updating a project you have already started, or making something new. Julie talks about how to find meaningful projects to work in in her aptly named Finding Ideas.
If you find dreading updating a project you've already worked on, consider what excites you at the moment and create something around that.
Don't use placeholder content in your designs
Lorem ipsum and real content have a vastly different feel, and people will notice this. When you use real content (text, images, profile photos and more) you will often find that it behaves differently than placeholder content like lorem ipsum or example avatar libraries.
When I'm designing screens, I write content for any words on the page (it doesn't have to be really good!)
If you need content for a long passage, try using open content found online or text from a copyright free book.
Show, don't tell
Creating a visual or small animation showing an idea is better than writing a few paragraphs about it. If you have an idea about a cool new way to transfer photos between phones, such as making an animation or even filming a video. Showcase your idea rather than explaining it in words.
A long write-up doesn't equal a better project
Think about if you can get more value out of spending your time improving the work over writing a lengthy case study about it.
Pro tip: Most interviewers will only read through a project for a minute or two!