Go to conventions, talk to other artists in person (though learning here helps too!), find out your style of building. I know some people who don't work on things at all, then they take 24 hours and build almost their entire costume, and others work on it every day.
Creativity is a hard thing to define, however, after building props 5-7 days a week for the last 6 months, I've had days where I've had to force myself to build/make, but it's okay, if you grow your "maker" muscles it will become easier and easier for you to get into it. Also, if the time isn't right to make it, don't be to aggresive in forcing it, if you need to take care of other things first, do them, then use the motivation you get out of finishing those things to start in on your armor. I've been cosplaying over 3 years, made one "kind of okay" suit (my own words, spartan wise), so I'm still not done with my goal spartan armor, so I can understand you there, but as everyone above has said, learn yourself a bit more and how you work and play off your strengths and minimize your weaknesses, and most importantly, have fun!
I'm already feeling overwhelmed, and I haven't even started my build. I still need to get an x-acto knife, printer ink, and likely more cardstock before I can start. I printed off the first 6 sheets to the shin of my Master Chief build, and I just don't know where I'm going to start.
All the pepakura I've done before just pales in difficulty compared to this. I get that as long as I'm careful and patient, I shouldn't face errors, but I'm just scared I'm going to screw up. Should I practice on a less difficult pattern first?