Hey there, i may be of some help. Ill start from the top down.
First things first, the screen lid you have needs to be covered up with glass. About 90% of it. It really helps to keep the humidity in. You can get glass cut for just a few dollars at ace hardware or local hardware store.
Second, you may want to consider creating a hard scape with the background. Or at minimal picking up one of those tree fern panels that fit the back. That specific tank should have came with something of the sort. This basically gives your frogs more usable space. Plus gives your plants and such more stuff to grab onto for vines.
Third, we'll talk about substrate. You need to learn how to create a "false bottom". The search feature on the specific site is really helpful. Just search "false bottom". A general over view of what the substrate should consist of is creating a drainage layer and then a layer of soil, moss, and then leaf litter. Right now there is wayyyy to much water in there. Dart frogs do not need any standing water and babies and some adults are well known for drowning (never would of thought a frog could drown right!? haha). Definitely remove all of that water in the bottom.
After your substrate layer and background is setup you can go ahead and plant the plants straight into the soil. I would then consider looking for some more wood features and hiding areas for your frogs. The more hiding spots, the more often you will see them =)
Fruitflies are the perfect stable for dart frogs. It is very important that you dust your flies with high quality vitamins.
Do you know what type of dart frogs you are looking to get? Dart frogs are really an awesome pet and experience but it is extremely important that you do your research before purchasing your frogs. Im afraid your frogs will not live very long if they were places in this current setup. But hey! Thats why your here and we're ready to help.
If you have gotten your frogs already, it is okay. But it is extremely important to start making drastic changes to their tank. I would recommend moving them to a temporary tank. It could be a simple plastic tub (bigger is better) with some wet moss and leaf litter for substrate and some plants. Just to hold them over until we can get this tank looking good! Keep researching and ask as many questions as you would like.
Here is a good video to get you started. I highly recommend all of his products.
https://www.youtube.com/watch?v=uEtn3di1Cz0