One thing our visual design instructors instilled in us was the ability to be creative on demand. Design (graphic, information, way-finding, etc) is a business. You don't have time to wait for the Muse to come in, she has to be on the clock. You might get a new client at 8am and have to present ideas for an identity overhaul by the scheduled lunch at noon. No, really, you've gotta do.
Sure, you're going to get it wrong (that's another post), but you have to present ideas. That means after the hour long meeting where you learn basically nothing you need to know and a lot about things that don't matter at all (like the hair gel the AD - art director - just switched to) you spend an hour doing "research" (now that means googling, back then it was sitting in your chair, head in your hands, thinking "OMG, OMG, OMG, OMFG!" over and over), which leaves you two hours to do a hundred thumbnails, twenty sketches, and three or more comps (doing this on computer now means the hundred thumbnails - maybe - and then right to the comps). And don't forget to include half an hour for paste up on presentation boards (or now, struggling with Powerpoint, merging with the sales materials being developed, and cursing BIll Gates' name unto the seventh generation).
Think I'm being overly dramatic? Heh. You probably actually won't get the assignment until 10 as the AD/Sales goes to get their second Starbucks. So, yeah, I gave you twice as much time than you really had. Now can you see why out of 24 or so fellow graduates, there's less than 5 of us still doing this two decades down the road.
The best job related functions you can learn is 1) be quick, 2) be precise (spelling fluorescent "flourescent" on the presentation to the lighting company won't keep the business, and your sales person doesn't know the difference), and 3) get the work out (all this wraps up to being competent, it's a rare job skill)
So, yeah, you can be creative when "cold." This is why it's important to be stocked with ideas and the creative pump primed by all the off-time research. Now, it's always better to allow the subconscious to masticate on something for awhile. Yes, the end result will be better with that, and if you're "inspired." The trick is being able to get "inspired" at the drop of a hat. That's a trick you learn by doing.
There are various group activities that can help you learn this trick. One is to have everybody in a group write the first line to a story. Then everybody trades and gets 30-45 minutes to spin out the full story. Now, more than likely you won't get a full story written, but you should be able to get the frame of it out (the voice, the overall thrust, somewhere at about 500-1000 words). Then everybody shares what they got. This exercise works because you're not invested in the story (it's not "your" idea - well, it is, but you can fool yourself) and there's a deadline, plus you need to share. You can see variations on the theme here (give everybody a character, a plot, a setting, etc, and have them write what they get in 30-45 minutes, pull a story from literature and write an extension/version/joke/etc based on it). Select any of the various "writing prompts" (Writer's Digest, Writing Excuses, there's several websites that have lists of them) and have at. After doing this several times you'll get faster and better with it. You'll also become more comfortable with being creative on the spot. It's like calisthenics for the Muse.
This post? I have a list of blog entries for this concept (what I learned as a designer translates to writing). I looked back at that list about 20 minutes ago and this post is a result. I can be "cold" and still write/design. That's what I learned.