Generally (and if you hear/see exceptions, I'd love to hear about them!):
The present continuous (to express the future) is used for future actions or events that have been arranged/planned: "I'm going out for dinner tonight"
The future continuous is used for: future actions/events that will be in progress at a certain time in the future: "By 6:00, I'll be eating a big steak at Joe's restaurant"
The future continuous is also used for: predictions or expected trends (in progress): "By 2050, most people will be driving hybrid cars"
Remember that sometimes, just like in any language, context is understood or assumed and you may not hear some of the markers that signal the choice in verb form. For example:
If someone just asked " Hey, can you meet us after work tonight?", the other might respond with "I'll be hiking up Grouse Mountain" (using the future cont. not the pres. cont.), meaning "At 6 o'clock tonight, I'll be hiking up Grouse Mountain". Both parties already know the "when", so it may not be explicitly stated, but is understood.
Hope that helps!