Need to know the species of mudskipper as there is some variation in parameters. For most of them though you will want high temps and humidity, Around 82F (78-88F) and a cover or spraybar along one side to keep the humidity up. Salinity should be around 1.010, pH 7-8.5. Substrate should be sand or very fine gravel, NOT SHELL, (very soft sand is best).
Put in several highpoints such as smooth rocks and driftwood as they are pretty territorial and squabble unless evertbody has their own place. As for plants, well as people have said, the mangrove is classic but maybe not practicle for you. Other plants that are used for brackish tanks are Java Moss, Java Fern, and the "Water Onions" such as Crinum thaianum and Zephyranthes candida, both are readily available online. The Z. candida is pretty cheap, running around $8 for 10 plants.
Mudskippers are carnivores and will eat many small meaty foods such as shrimp or clam pieces, they also like small earthworms, crickets, and live ghost shrimp.
Well, thats about I can think of offhand.