Best of the Best
They say, "Save the best for last.", and that works in a lot of cases, but not with photography. Always show your best work first. If you only have the chance to show off one image, make sure it's good enough to grab and keep a person's attention long enough to show more of your work.
15 Second Elevator Pitch
It's just like the elevator speech. Can you impress them before they reach their floor and exit the elevator?
If you only have 15 seconds of a person's time, you'd better blow them away. I have a picture that I always show first, no matter what. It's a photo of Janet Jackson. The colors are really vibrant, it's in-focus, the composition is nice, Janet's cleavage is present, and after all, it's Janet Jackson - she's a legend. That photo always keeps the person's attention, and they always want to see more.
I actually keep my phone, in my back pocket, open with my photo galleries ready to show. If I'm backstage at a concert, I have the "My Concerts" folder open with the Janet Jackson photo highlighted, and ready.
When showcasing your work online, limit the amount of content you post per event. If it's a photo recap from a concert, don't post 47 pictures of the performer, when 6-10 images can tell the story enough. Unless of course, you're telling the entire story, including images of the band members, if the performer changes outfits, the crowd, signage, etc.