This is a tricky question. There's very few wrong answers.
Aquascaping is varied, there are some "rules" that can be helpful, but the fact of the matter is that it's art. And like art, there's millions of ways to do it and can still call it art.
The first suggestion I'd say is to look at various styles. What style speaks to you. Do you like a natural nature setup? Jungle setup with a ton of plants scattered everywhere? A more decorative garden without hardscape such as a Dutch style? Perhaps you want to go as natural as possible and go with a biotope style? Perhaps you like blackwater type setups with tons of leaf litter and dark stained water? Or, go for a creative spin and make fantasy type setups such as a forest, hills, or cliffs? Something more riverine, such as a hillstream aquascape? There's sooooo many styles. I would search all of them on Google to see examples and see which appeals to you the most to start off. Keep in mind, some styles will impact your fish choices as not all fish will be happy in every setup. Iwagumi setups are beautiful but they lack cover and shelter for fish, so majority of fish will be stressed out in an open layout like that, you'd be limited to fish that naturally are in open habitats. Likewise, bottom dwellers may struggle to enjoy a carefully scaped forest because many play on optical illusion using vertical space, which will use up bottom space that bottom dwellers enjoy.
Next is placement styles.
There are island type scapes where the hardscape and plants are restricted to a small area surrounded on 2 sides being open. This style looks most effective with cube style tanks, but can be done with long scapes as well, or even creating multiple islands in longer scapes. Cube style or tall tanks are restricted on fish choices as they'll need to be stocked like a smaller tank due to their shorter lengths for swim space. Something to consider as well.
There are triangular scapes which have plants and hardscape tall at one end and it tapers downwards in one direction. These are great in long setups.
A U shaped scape has plants and hardscape taller on 2 sides which lower as they meet in the middle, this can also include having a small valley between two scaped sides.
Placement creates "movement" in your scape. Plant and hardscape choices will reflect this. Want to create a faster looking scape? Round river rocks and long grass plants will create this. Angling wood in ways that they look like they're going with the current will amplify this movement. Or want a more tranquil still looking scape? Soft, fluffy plants and plants with lots of round leaves can grow vertically and create a soft appearance.
All of these can overlap. There's no right or wrong, it comes down to personal taste. I like to change around some stuff, I can share some past examples I've done in older setups or even a couple current ones.
Some examples of an island style scape:
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Island x jungle
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And island placement nature style
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This one is a U shaped scape (once the right side fills in like the left side, anways)
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An island style blackwater
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Jungle style
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Triangle style natural
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Nature triangle style
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Biotope triangular scape
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Biotope blackwater
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Island style
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Island style
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Biotope planted
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I play more on the natural side of things, and have increasingly moved towards natural/biotope styles because that is what I am drawn to.
Some general rules:
Tall plants should be placed in the back or the tank. Shorter plants towards the front.
Factor in the fish you have/want to have when planning the scape. Some fish do better with certain setups, while some others won't allow you to have some setups at all. For example... Slopes won't stay if you've you've digging fish. They will inevitably flatten the slopes. Some fish will eat plants or dig plants out.
It helps to watch videos of fish in the wild to get an idea of how they behave with their environment and try to recreate that with your scapes, even if they're not natural scapes. You can be creative in offering a home they can interact with.
When choosing hardscape, try to stick with the same. For example, don't mix dragon stone with river rocks. It won't look uniform. And when placing dragonstone, place all the ridges in the same direction.
Wood of the same color and texture is helpful, but can vary a little if you opt for natural or biotope scapes.