Dissonances need to be written very carefully. While many inexperienced composers write in a way that they just add “random” notes to a sound in order to make it dissonant, it will most likely result indeed in a very dissonant sound, however possibly with very little transparency and become very thick and unfocused.
Well written dissonances are mostly very transparent and feel very “fitting into the texture”. Here, also the rule of less is more applies. You can create fantastic, dissonant and very transparent sounds with as few as three or even two notes which will always have more musical quality than just writing a block of notes that in general create a very thick, unfocussed, unidentifieable wall of sound.
In general, larger intervals between notes make things more transparent than smaller intervals, which will create more of a cluster-effect. Certain intervals like the minor ninth have a very heavy degree of dissonance and therefore are able to add a tremendous amount of dissonance by just adding one note.
On a multiple note dissonance structure you can handle the degree of dissonance by increasing the number of dissonant intervals within the structure. For example THIS three-note structure has a much “tamer” dissonance degree due to the major sixth between c and a and the major third between a and c# than THIS structure, which has apart from the same minor ninth frame interval an inherent major seventh and major second. The difference is just one note on that already dissonant structure but still it makes a very strong difference.
A great exercise to practice this would be to write a dramaturgic arc with a “dissonance buildup”, where you start with a mild dissonance and gradually work your way up to a very strong dissonance without changing much of the texture/dynamics etc. By that you learn to take control over a composition principle that diverts quite a bit from traditional harmony but still can be understood by general audience and creates an emotional impact.
Of course, here I can only scratch the surface of these things, to dive deeper into this topic, I highly recommend Vincent Persichetti’s book “Twentieht-Century Harmony”.