If you’re new to cichlid keeping, one subject you might be trying to learn more about is the appropriate tank decor for the species you keep. There is no shortage of information and advice available online. Plenty of folks have written about decorating a cichlid tank, and much of this consists of do’s and don’ts.
If you’re wanting to emulate a biotope specific to your fish (e.g., Lake Malawi), another natural environment, or provide the optimal aquascape for breeding particular species, then I encourage you to heed some of the information out there. However, if you don’t have any specific intentions other than to keep some cichlids for your own viewing pleasure or that of your friends and neighbors (i.e, a show tank), don’t obsess over the decorations.
For the most part, the choice of ornaments, rocks, plants, etc. that occupy the same tank space as your cichlids are important only to you. Clearly don’t put things in your tank that might affect the quality of the water. Otherwise, make it look how you want it to look.
With that out of the way, I would encourage you to include SOME decorations, substrate, etc. A completely bare show tank provides nothing for your fish and has the potential for adding stress. Cichlids, just like other fish, will instinctually seek shelter to avoid predators, threats, etc. A bare tank offers nowhere to hide other than behind whatever hardware you are using (e.g., filter tubes, sponge filters, heaters). Though my fish will typically congregate near the surface when I approach the tank to feed them, they will also often scatter and or display skittishness many times when I merely walk by. When this occurs, they’re rushing off for a safe place to hide. What comprises that place isn’t really important to them as long as it provides enough shelter to hide them from view.
Therefore, give them some places to go when they’re frightened or otherwise stressed. You can do this with submerged PVC components (tubing, connectors, etc.), ceramic decorations (pagodas and other ornaments), rocks, plants, and other things. Substrate choice isn’t as important except that bare glass is reflective, and reflections might have adverse effects on your fishs’ behavior.
I know some expert cichlid keepers who are a bit whimsical with their tank decorations, some who are minimalists, and others who are naturalists. Largely, your fish don’t care how you decorate their environment as long as your choices don’t introduce additional stress. It’s been proven that stressed fish will typically exhibit muted colors or otherwise won’t look their best.