I have a 17L tank that effectively has maybe 10L of water, in which I keep small guppies (offspring from my larger tanks) until the outgrow it. It's sitting on a bookshelf in the hallway, completely unheated. I use a regular Philips 13 W 4000 K LED (around 1.500 Lumen) mounted in an Ikea desk lamp as lighting. For filtering I use a backpack filter (AquaClear) filled with ceramic filter material with high surface-to-volume ratio and some fine polyester wool. I prefer these types of filters for small tanks as they hang outside of the tank and dont't use up any space inside.

The most important thing for a healthy aquascape is to have many healthy plants, with some fast-growing ones that will take up any excess nutrients. For an open tank I recommend water lentils (they can get out of control fast though) or swim ferns like Limnobium Laevigatum or Salvinia Auriculata (beware of the shade they create). In my tank I also keep Hydrocotyle Tripartita, which looks great in an open tank that can be viewed from above, grows fast and forms a nice carpet that doesn't grow too high(unless it doesn't get enough light, in which case it will grow mostly vertically). I also keep two Echinidorae Ocelot, which are really easy and form a dense system of roots. Finally, I have some Limnobium Laevigatum as a floating plant and a small carpet of Hemianthus callitrichoides Cuba (HCC), which is rather complicated to keep and requires good CO2 injection (I use a plastic bottle with a yeast-sugar mix and a small upturned glas bowl in the tank to set CO2 at 25 mg/l). Having some root-forming plants is important as the roots will keep the ground from becoming anaerobic, which can lead to a foul-smelling aquarium. As substrate I use volcanic gravel below and regular gravel (2-4mm grain size) above, possibly with some nutrient-rich soil above (this will help e.g. with HCC but isn't required). For a small tank I'd go for 3-5 cm of substrate at most. You can have more but you'll need to ensure you have root-forming plants in most areas that keep the substrate aereated. I fertilize with micro- & macro-nutrient fertilizers every couple of days. Lighthing is turned on for 11 hours. I feed the fish (12 small, not fully grown guppies) once a day and am careful not to overfeed. I also keep 10-20 ramshorn snails (they can reproduce quite fast but if you don't overfeed your fish their numbers stabilizes quickly).

Sakura shrimp are quite easy to keep as well and will reproduce without much effort, larger fish (even fully grown Guppies) will see the small ones as food though and stress the large ones enough to kill them, so beware of putting them in a tank with fish.

In the first 2 weeks you'll see a lot of brown silica algae form everywhere, which is normal, usually followed by some green algea. Which types of algea you'll get depends heavily on your water parameters though (hardness, mineral content and contaminants), I have hard, nutrient-rich water and get mostly green algea, other people see brush or black algea instead. After 4-6 weeks they should mostly disappear as the plants start to grow rapidly and take up most of the nutrients in the water, starving the algae.

So to summarize:

- Use lots of healthy plants, at least some of them should be fast-growing (you can remove these later if you don't like them). There should be as many plants as possible, while making sure they don't shade each other. Great fast-growing plants are e.g. stem plants like Hygrophilia Polysperma, Rotala Gia Lai / H'Ra (one of my favorites) or swimming plants like Hydrocotyle Leucocephala (which is not very suitable for small tanks though IMHO). A great carpet-forming plant is e.g. Marsilea Hirsuta, which grows quite well without CO2 and low lighting.

- Don't overfertilize in the beginning, start with 25 % of the recommended dose and work upwards.

- Start with 8 hours of lighting and work your way up to 12 hours during 4-8 weeks.

- Add snails or shrimp after 1-2 weeks and fish after 2-4 weeks (not too many at once). Be sure to select fish that are suitable for nano aquariums (opinions diverge here but IMHO you can easily keep e.g. smaller Guppies in a nano tank as well).

- If the tank develops a serious algae problem (e.g. blue algae) block out all light for 3-4 days, this kills most types of algae and can give plants an advantage as soon as the lighting comes back.

- Only clean the filter when you notice the flow is drastically reduced. Don't wash the filter material with hot water or anything, just press it out in a small bucket/bowl of water from the aquarium until most of the coarse dirt is gone. The filter bacteria are the most important part of your tank, so treat them with respect.

- Have patience, the tank will usually look quite ugly for the first 4-8 weeks, so don't give up easily.