Dither fish are fish (usually smaller non-centerpiece fish) that make the larger fish feel comfortable by swimming around happily. People usually use fish that are not shy and are quick-moving. To me, other cichlids in the tank are usually not dither fish, they would be "target fish: if their purpose is to distract aggression and they are large enough for the main fish to see as a threat.
Personally I decide what the dither fish will be for cichlids based on region. If the cichlids are central american, I go with livebearers like the common molly, swordtail, or platy, even the less common goodeids. If the cichlids are from south america, tetras for smaller tanks and silver dollars for 100g+ tanks. Plenty of other SA oddball characins that could be used in larger tanks as well.
Most African cichlids really don't require dithers, I have yet to meet a shy mbuna when stocked properly with a bunch of it's buddies in a large enough tank. When kept singly or in small numbers of other species, they tend to be shy, but instead of adding other dither fish, I would get more of the same type of mbuna, because they prefer to live in conspecific groups. Perhaps for fish like frontosa, smaller cichlids could be effective dithers.
carsonrm01
tell us about your setup (tank size, stock) and we would be able to recommend a dither. Without that info, recommending anything is just shooting in the wind.