they need nutrition just like any other living thing 
Any fertilizer that may have been in the soil when you first bought the plant gets "leached" out by regular watering. Also, plants tend to get "leggy" when they do not get enough light and have to "reach" for it. Typically, any plant (especially house plants) that flowers needs good light and proper fertilizer.
The hibiscus should be one of these two species since they are more adapted to indoor situations: Hibiscus rosa-sinensis or H. schizopetalus. Hibiscus needs a fertilizer with high potash content (what the heck does THAT mean??) It is actually simple. Buy a soluble (one you mix with water) fertilizer (Peter’s is a good brand). There are always 3 numbers on the label: 10-10-10 or 5-7-5, etc. What this means is the ratio of Nitrogen, Phosphorus and Potassium (potash) – in that order. This is an industry standard and ALWAYS is the same. If the plant gets leggy just prune it back to just below a leaf node (where the leaf comes out of the stem) or just above a crotch (“v”) and it will stimulate it to branching out and making a more bushy plant. (Hibiscus, not Ficus)
Is your Ficus a F. benjamina or F. elastica (aka rubber plant)? The benjamina is the one with smaller leaves and they often have “braided” or twined trunks it is also prone to scale insects that congregate under the stringy bark. They also ALWAYS have some leaf drop but will grow back.
The easy all round solution is to get Peter’s with a higher 3rd number OR one with all the same number (20-20-20). Follow the directions.
As for general watering….more plants die due to too MUCH water than not enough. My suggestion is to get a couple good books on indoor plants to add to your cham book library.
Hope this helps!
lele
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0.1 veiled - Luna
0.2 green anoles (Jaida, no name)
0.1 brown anole - Jamaica
0.2 house geckos - (still no names)