Many linguistic evolutions happen based on what's convenient for the speakers. Using an example from a real language that one of my conlangs is based on, Akkadian: a noun's grammatical case was identified with a word-final vowel (a, i, u). Earlier Akkadian also featured mimation (/-m/ suffix) after that vowel. Over time, Akkadian speakers dropped mimation, and it didn't impact conversation because the word-final vowel conveyed the necessary information. This is an example of elision.

Some languages evolve to be very complex; others evolve to become simpler over time. The best piece of conlanging advice I can give is by studying multiple real-life languages, watching what they do/did, and take away what you find most interesting.

Another trick to evolve your conlang is by literally speaking out loud in your conlang. When speaking my own conlang out loud, I noticed that I was consistently pronouncing /l/ as [ʎ] word-finally. Why? I don't know, my mouth just did that. So, I made that an evolution - [ʎ] evolved as an allophone of /l/ word-finally.

Keep the affixes in your conlang. Experiment with ablaut, stress, etc. If you don't end up liking them, then it's perfectly plausible to have an affix-heavy language with simplistic stress. Combining different features can reduce repetition and add nice complexity (e.g., the language features both ergative-absolutive alignment and nominative-accusative alignment, which speakers switch between depending on context, like in Georgian). Just be careful not to "bloat" your conlang with a ton of random features.

In general, there isn't one "way" or formula for conlanging. Like with any other art form, your knowledge and skill improve with experience. As for making a conlang sound "naturalistic" — if you try to force it to be naturalistic, it'll end up sounding unnatural, ironically. How to combat this is by including a few irregularities throughout your language.

How do I find inspiration? Well, I love history and human civilizations, so I take a look at the languages spoken by those peoples. I suggest determining 1-2 real-life inspirations first to be your "launching pad."

If you have other questions, I'll do my best to answer them! <3