When you submit images for a photographic competition, there are a number of requirements expected in order for them to pass certain criteria and 'technical merit'.
An image must be befitting its title. For example, a portrait or portraiture refers to photographs taken of a single person, a couple, or persons in a group. Such as photos taken at weddings, functions, etc.
A landscape must depict a vista image of the land. Seascapes can also come into the category of landscapes.
Other subjects or topics might be Nature, Cityscapes, Nightscapes, Architecture, Pictorial, Silhouettes, Social Documentary, Sunsets, Sunrises, etc. They all must display clear evidence of their subject and title and whatever category they fall into.
The best landscape image should show everything in clear focus. From the front elements, all the way through to the distant background. And for impact, make good use of light and colour.
It is also a requirement to display a sense of depth with a foreground, middle and background elements, showing a strong centre of interest, as well as other subordinate subject matter placed at strategic points ('Rule of Thirds') within the image to allow for good eye flow throughout. Taking into account the elements of photographic design, such as light, colour, lines, shape, form, etc., all of which can be referenced on this site in 'Composition Design'.
Also important are straight and level horizons and remembering the 'Rule of thirds'.
Nature photography should comprise only of natural flora or fauna excluding all cultivated plants, domesticated birds or animals and exclude almost anything to do with humankind. Such as fence posts, power lines, mowed lawns, buildings etc. However, it is accepted to photograph Barn Owls in barns because a barn is a natural habitat for that particular bird.
Fill the scene with your subject and as with people photos, it is important that you concentrate your focus on the animal's or bird's eye/s.
Black or dark backgrounds are generally frowned upon. By using a larger aperture you can lightly blur the background to put the emphasis on the subject, but keep the habitat distinguishable.
Or, if the idea is to show your subject complete in its own habitat, you will need to set a smaller aperture to achieve a greater depth of field.
But, remember to 'keep it simple'. That's important!
Landscape and nature seem to be the dominant subjects for the majority of those out taking photographs these days, apart from family photos of course, but there are certain rules that apply in all topics of photography and if you do intend submitting your images for competitions, you would be well advised to be fully informed on all the required criteria for your particular field of photography.
See my chapter on 'Rules For The Rules'
Include in your portrait photograph your subject's place of work, where possible, this will create an interesting picture story about your subject.