Before you get darts, be sure you will be ready for the task of feeding them.... It sucks. As for all other aspects of dart keeping they are pretty simple. What size tank are you looking for? What I like to do for vivariums is to first buy black silicone - no mold inhibitors of course! Spread it on the tank's background and sides if you end up using them. Then you buy "Great Stuff" insulating foam and you can use this over the silicone to make a "hardscape" in the tank. When you are done with that, you need to coat the entire background with silicone again and press into it dried coconut fibers, peat, whatever. This whole process takes a few days with all the curing times. If you get good with this method, you can use the foam to make cool ledges, and planters, etc. Also, try to give some space at the bottom of the tank's background. This way you wont be wasting a ton of the great stuff where you can't see it. There are some easier backgrounds to use like tree fern fiber but I don't recommend it as it's a non renewable natural resource....so yeah. Another one which is cheap and not bad looking but I never got a chance to try.... In the aisle where they sell hermit crab junk, there are rolled up cocnut fiber mats that you can silicone onto the back of the tank. Next you need drainage. Buy enough clay pellets online, or from hydroponics stores to fill the bottom of the tank 1"-2". I can't remember what they are called....
Anyways, cover them up with some fiberglass window screen. Next step is substrate. This depends completely on the plants you want and your personal preferences. I like to mix a large amount of peat, some coconut fiber (bed-a-beast), some orchid potting mix (I use Better-Gro Phalaenopsis mix), and a little bit of potting soil, maybe some sand if you like. Now, plant the tank however you want.You can try the fly trap, although most carnivorous plants don't mix well with Dendrobatids. Go to loews, or home depot and they can cut some glass for you to make a lid for the tank if you can't find anything suitable. Just remember, the fruit flies can escape anything!
You don't need a background, but it looks really nice and gives you the opportunity to add climbing vine plants which will cover the background, etc. Oh and always tru to use distilled water! It is fine for the frogs, and it doesn't leave water marks on your glass!
You can also go a cheaper and much easier way if you prefer. This is more for breeding than a vivarium. Take a tank, fill it with small gravel, make hills, or whatever you want, and cover it with your substrate, a screen over the gravel would be helpful also. Plant the tank with simple plants like pothos, add frogs. If you can get good clean dried oak leaves they make a good addition to either potting mix or even a floor covering. I recommend adding springtails to your tank also, and letting them get a good population before adding frogs. They help clean up and are a food source for smaller darts. Hope this helped! Enjoy.