I'm somewhat against just going in half-cocked with no knowledge and messing around with things you don't know what are, and expecting to get good results consistently.
I recommend learning what exactly each element does. In other words, learn the physics with how the oscillators interact, learn what an LFO is, what different filters and effects do, etc. Even the math behind it can be both fascinating and useful!
You can find all the info for free online (Wikipedia, blogs, google, etc.), or you can be a bozo like me and get this, which gives a nice little intro to synthing in the first chapter:
http://www.amazon.com/Dance-Music-Manual-Tools-Techniques/dp/0240521072/ref=sr_1_fkmr0_1?ie=UTF8&qid=1376299396&sr=8-1-fkmr0When first starting out with learning synthesis, read that crazy manual that came with the software!
I can recommend you focus on Massive at first and nothing else because you have it, and it gets the job done. It may seem a little intimidating at first with all kinds of knobs and charts everywhere, but when taken one element at a time, you may find yourself wishing it had more! Once you get a hang of how things work, new synths feel simply like driving a different car. There's no use synth hopping all over the place and never learning what you are doing.
Here's just a few ideas for learning your sound design:
Try to copy real-life sounds
Try to copy a sound you make up in your head
Practice.
Try to copy a favorite sound out of a record you love
Take your synth to the max! leave no oscillator, filter, or effect unused, no knob unturned just for fun.
Practice.
Evaluate a favorite preset and strip it back down to nothing. Then rebuild it with what you remember!
Open up two different synths, and try to copy one preset into the other synth to the best of your ability. You can try it with or without looking at the other synth.
Experiment! Try new things at a whim, or with previous knowledge, or both.
Don't be afraid of using presets as building-blocks for learning new aspects of sound design. Make sure you know how to evaluate what you are looking at.
Practice.
Read blogs and articles.
Watch youtube tutorials.
Soak up any information you come across.
Practice!