So I put up a couple hummingbird feeders. Now what? Is there anything else I can do to attract them? Do I just have to hope a hummingbird flies by, sees the feeder, and tells his/her friends?
Load it up with vodka and/or NyQuil? 
There are flowers you can plant which attract hummingbirds.
Hibiscus work well–may not be cheap or convenient for you.
Verbena
Anything which has lots of small blooms, and nectar down inside, so that the hummingbird goes from blossom to blossom. Red is a popular color. I’m certain my mother has a couple more favorites which she plants, but I can’t tell you what they are off-hand.
Ignoring the hibiscus, for a moment, most of Mom’s get planted in pots which sit on the deck, get watered frequently, and with a little bit of luck last from May to September.
I second the idea of putting some pots of red flowers near the feeders to help get their attention. Bright red annual Salvia is another good option.
Even though I wasn’t trying to attract hummingbirds, I watched one attempt to feed from my seed feeder last year, just because the feeder has a red base. 
Put the sugar water in it, and wait. We already have Hummers comming to ours in CT. An of course they love RED…LOTS OF RED
You might not have heard – but they love the color red.
Also, they like trumpet-shaped flowers (petunias, foxglove, trumpet vine). Buddleia (a bush) is another good choice – it’s known as butterfly bush, but that’s because it’s loaded with nectar, so attractive to hummers as well.
We have a few of these [butterfly bushes] floating around the yard…last year I was mowing the lawn and stopped to gawk at a hummer feasting on the nectar - then I saw it wasn’t a hummer but some sort of moth. Do you remember the name of those moths that look like hummers?
They are called hummingbird moths like these?
It can sometimes be hard to get the first hummers to start showing up but they will come back for years once they know about your feeder. Just remember to change the sugar water every few days.
One buzzed by my head while I was out in the yard last week. I filled the feeder, hung it up, and he was busy at it after about 5 minutes.
Oh, by the way, they like the color red.
I wonder if they have a favorite song from, say, Duran Duran.
Rojo, by Duran Duran? 
It can sometimes be hard to get the first hummers to start showing up but they will come back for years once they know about your feeder. Just remember to change the sugar water every few days.
Um, if you want to attract Hummers, you might want to fill the feeder with gasoline
(ducks and runs)
Red is so last year.
All the hummingbirds “in the know” will be looking for chartreuse this season.
Thanks for the suggestions. I now have some good ideas for plants to put on the patio. I’m thinking perhaps I’ll buy some red flowers. . .