Hey Jkessler,
First, be sure to check state regs before you take fish home! Know the rules, and know how to identify fish that cannot be legally collected. For example, taking home a protected Spotted Darter could get you in trouble, as could an invasive Round Goby.
The best way to catch most darters is with a seine. You'll need a partner for best effect. It's good to have an experienced seiner help you out the first few times, until you get the hang of it.
Different darter species can be found in different microhabitats. Some will be in swift runs or riffles, some in pools, some along banks, some in deep channels. A few darters like big rivers, lakes, swamps, etc., and many like headwater streams and springs, but the best diversity can be found in mid-sized creeks.
Darters are not in full color all the time; they are at their brightest during breeding season (usually April and May here in TN) and are a little drabber the rest of the year. To keep them colored up in the tank, it's a good idea to keep the water fairly cool, say in the mid-60s.
By the way, Creek Chub do not play nice with others. They are not a good tankmate for darters or for smaller minnows, though they can do all right with other big minnows and with sunfish.