If you really need to learn JavaME from Java SE, then you should read an old Java SE 1.4 book, and just stick to the basics of the language.
Why? Well Java ME is based on JRE 1.3, so there are no generics, no collections (added in Java 6) and let alone Java 8's new stuff. If you buy a recent Java SE book, you might get confused because you won't be able to use these new features.
Second thing that differs, it is not an homogeneous platform. It is divided in two parts (CLDC/CDC for the core classes, and MIDP for the GUI classes). And there are optional profiles (JSRs) that migh or might not be supported in a certain device.
Other than this, you should always keep an eye on memory efficiency. Old devices do not have much RAM, so you should never try to load large images or data in memory, and always free resources when not used.