I have a old LG MG280 cellphone that I'd like to code some simple things for. It has Java support, but I know that it is not simply making a Java ME application. It has to follow some specific specs otherwise the app will not run. Does anyone know what those specs are?
Find out which J2ME profile it has - MIDP etc. Then find an appropriate tutorial, such as this one.
JavaME platforms are made up of a profile and a configuration. Most mobile phones use some combination of the Mobile Information Device Profile (MIDP) and the Connected Limited Device Configuration (CLDC).
The LG MG280 you are interested in uses MIDP-2.0 and CLDC-1.1, which is pretty standard.
To get started with development you'll probably want to be using the Sun Java Wireless Toolkit (frequently abbreviated to SJWT or WTK). Or, if you are a windows user, you can use the (newer) JavaME SDK 3.0. This gives you tools needed to compile/package applications and an emulator which lets you run/debug application on a desktop computer.
There are numerous tutorials available online. Here's a few to get you started: