1. Work at Your Level. Have basic sewing skills? Don't overcomplicate your case design. Think a rectangle with 3 sides sewn and one open, with no lining, in an easy to sew fabric.
2. Choose Your Fabric Wisely. One of the joys of going custom is being able to pick out the fabric you want to use. Choose a print that you'll enjoy looking at in a fabric that is at your sewing skill level. Of course, since this is a tablet case, make sure that the fabric won't scratch your device.
3. Be Prepared. As with any DIY project, have everything you need to complete the project at hand before you begin. It won't be fun to be halfway through the project and realise you're out of thread or you can't find the materials you need to finish the case.
4. Practice. You know how on Project Runway you see designers using muslin to get the fit/pattern right before cutting into the fabric they are going to use for their dress? If you're unsure how the case is going to fit, use muslin first to make the case. By making the case this way, it will also give you the opportunity to work on your sewing skills a little more and be better prepared for the corners.
5. Think Closures Through. Decided that your tablet case really needs a closure instead of being a simple sleeve? Think carefully about what kind you want to use. How it will work with your chosen fabric and how it will function when the tablet is inside? I have come across several DIY tablet cases which caused screen damage because of the chosen closures. A good rule of thumb: avoid snaps, and be careful with velcro!
(Image 1: Joelle Alcaidinho, 2 & 3: Melissa Alcaidinho)