My first project was to reproduce an object that was made of a different material but would work well as a laser project. I posted my first steps as a topic and got loads of help from the forum. The topic developed and I was able to design an object that worked perfectly th first print. I had a little experience using vector drawing programs and had been using Sketchup before so that helped.
Right now I am looking at a ceiling fan above me and thinking that I could make some cool, decorative fan blades with the Glowforge.
You could always just start with making cutouts of different things. I think the coaster idea is interesting. Whatever you decide, don’t be afraid to show your steps or share your mistakes or problems. I think many forum members are eager for something to do. As long as you show something. Even if it is a napkin sketch and you ask the question: how would you turn this into a file the Glowforge could process. I did that with the basketweave engrave and was so delighted to get all kinds of ways to improve the process.