The over all consensus seems to be that anubias plants and swords are the easiest beginner plants. They can get fairly large, but tolerate trimming as well as a wide range of different lighting and water conditions. They’re also quite nice looking plants.
There’s a list of aquarium plants and their basic care requirements here to give you a better place to start your research 🙂
Get yourself some Java moss and Java fern, they’re nearly impossible to kill. Neither should be planted in the substrate, just tie/wedge them loosely against wood or rocks and they’ll grip on.