Consider your tap water parameters before buying plants. Some like soft water, some like hard. Also temperature plays a part, some like low temps and others like hard. Some will require fertilisers. Other will require lots of light. Do some research on each individual species to have a better chance at keeping them alive.
I recently bought elodea densa and put it in my tank. It started dying because although it was good for my water parameters, my tank was too warm for it so i have it outside in a bucket. I also bought a dracena plant as recommeneded by my LFS. It too started dying and i have since found out that it is not an aquatic plant, so be careful. It is now in a plant pot