This is going to be an individual thing. I remember Yates saying somewhere many moons ago that he found that if he ate certain things (carbs?) too close to training, he felt his blood sugar would drop.
Personally, I used to subscribe to this, because it sounded reasonable, but quickly I found that not only could I tolerate certain carb sources close to training, but that I could handle a lot and actually have a better focused workout.
Lots of good suggestions given so far. I know that while I was never really the monk-like guy with the hoodie or hat, I always had my headphones on from the moment I entered the gymm until I was walking out. The eye-contact thing helps, but remember to not be a dick. Serious trainers will understand, but other people may mistake you for being rude. Learning how to be focused, yet mindful in a public facility is key.
Getting back to the music/headphones thing, an obvious product of the 1980's, and the "mix tapes" for every event, I've really taken to the Ipod playlist feature. I put together a playlist back in early 2011 that included every damn song (no matter how old or silly) that somehow got me amped, or even just spoke to that part deep down inside of me that makes me go the extra mile. When I ran track in school, I was similarly influenced by music, and could run for hours if I had a good tape (a f-cking cassette tape!! -lol)
Other things you'll hear people suggest (mostly women on Opera though), is new workout stuff. Now I'm not the type who walks into a gym hoping everyone notices my new tank top, but there is something about catching your reflection mid training, seeing the muscles all pumped up, face still reddened from the last set, and sporting a sleeveless and shorts that accentuate your physique just right. In moments like that you think to yourself "yeah, there's a reason I've made this progress while others ar floundering", and you dig in for another gruelling set.