looks to me like your plant needs a lot of TLC. First off I would get rid of the dead or dying leaves. Second I would test for the following....NitrAtes, Ammonia, phosphates, NitrItes, pH, iron. Now for plant care 101....
Plant care 101:
Live plants need Nitrates and trace elements to live off of. These are their food. If you don't have these your plants don't grow and die.
They need iron to help in their photosynthisis. There are some plants when they look like they are yellowing they need iron. Iron is more important to plants than most people realize.
CO2 is a good thing to have with planted tanks. This helps them grow like crazy and well it doesn't take long to have a jungle when you use CO2. It's not necissary but plants like it.
Fast growing plants are a must in any planted tank. These help keep algae under control by out compeating the algea for food.
Lighting will depend on what plants and size tank you have. Most lights need a minimum of 2 watts per gallon (US gallon) to grow.
Depending on what plants you have some are root feeders. Meaning they need a nutrient rich substrate (laterite mixed with gravel or something like that). While others have poor root systems and get their nutrients from the water its self (in the form of fertilizer).
You put all of these things together and you have an aquatic jungle for your fish to be happy in.