The plugin docs are a good reference but can be a bit daunting when piecing things together, any good plugins from the community that are well commented/built etc. ? Especially in regard to elements.
Mijingo has a great video on plugin development at https://mijingo.com/products/screencasts/craft-plugin-development/
Outside of that I'd take a look at the plugins at https://straightupcraft.com/craft-plugins/