Drywall is a suitable substrate for the glass tile. You want to make sure that the drywall is clean, wipe it down with mineral spirits. Next you will want to mark a level line. 1" Glass Tiles are fairly heavy when mounted on a 12" mesh sheet, and will tend to sag. This level line will be the top mark of your lower sheet. After you have your line either drawn or chalked, you will want to use a glass tile specific mortar, such as Mapei Adesilex P10. This is a non sagging mortar with a bright white color to allow the glass color to pop. Be sure to follow the mixing instruction to get the best performance, and only mix as much as you can use in a short period of time. Glass tiles are great for backsplashes because of the ease of maintenance, so make sure to use a grout that give you the same performance. Mapei has Opticolor grouts which are stain-free, but offer the same installation as regular grout. Last bit of advice is to be patient, work at your own pace, and step back every other sheet to make sure it looks good as you go.