First things first, does your tank have all the necessary equipment and do you understand the basics of fishless cycling and water quality?

I'm assuming you want a common plec and a selection of other large fish such as cichlids? Unfortunately your tank will be too small for these, common plecs (Liposarcus multiradiatus) can top 18"/46cm and will grow far too big, most of the larger cichlids and other fish growing bigger than 5-6"/13-15cm will also be too big. I would recommend fish that grow no bigger than around 4-5"/10-13cm. If you did add a large selection of fish that grow bigger than the sizes already mentioned you will have serious problems with overstocking, which in turn will cuase water quality problems.

However there are some smaller cichlids available such as Kribensis and Keyholes that would be suitable for a tank of this size, both of these fish grow to around 4"/10cm.

If this is your first tank I would stick with the peaceful community fish such as platies, tetras, anabantoids (i.e honey gouramis) and small catfish such as corydoras and smaller plecs such as Panaque and Hypancistrus until you learn the ropes. Once you are able to obtain a larger tank (at least 72"/180cm for a common plec) you will be able to start keeping some larger fish.