quick tips for creating fantasy language(s) that look believable if you squint
Pick a few rules about what letter/sound combinations can and cannot exist (or are common/uncommon). For example, in English, "sp" or "st" can begin a word, but in Spanish they can't. The "ng" sound (or the voiced velar nasal if you want to get technical), can't appear at the beginning of a syllable in English, but it can in at least of third of languages around the world. English allows for consonant clusters (more than one consonant together without a vowel), but some languages, such as Hawaiian, don't. Picking a few distinctive rules that are different from English or the language you are writing in, and sticking to them, will yield a lot better results than just keysmashing.
Assign meaning to a few suffixes, prefixes, or roots. A simple and useful example of this is making up a particle that means -land or -city or -town, and tacking it onto your appropriate place names. You could also have a particle with a similar meaning to the "er/or one we have in English, such as in "baker," "singer," or "operator," and then incorporate it in your fantasy titles or professions. It's like an Easter egg for careful readers to figure out, and it will make your language/world feel more cohesive.
Focus on places and names. You usually don't need to write full sentences/paragraphs in your conlang. What you might want to do with it is name things. The flavor of your language will seep in from the background, with the added benefit of giving readers some hints on background lore. For example, you could have a conlang that corresponds to a certain group of people, and a character with a corresponding name could then be coded as being from that group without having to specify. A human-inhabited city with an elven-sounding name might imply that it was previously inhabited by elves.
You don't have to know what everything means. Unless you are Linguistics Georg R. R. Tolkien, you probably don't want to (and shouldn't!) actually make up a whole language. So stick some letters together (following your linguistic rules, of course) and save fretting over grammar and definitions for the important stuff.
(Bonus) This isn't technically conlanging, but it can be fun to make up an idiom or two for your fantasy culture (just in English or whatevs) and sprinkle that in a few times. The right made-up idiom can allude to much larger cultural elements without you having to actually explain it.
Congrats! You now have a conlang you can dust over your wip like an appropriate amount of glitter. Conlangs can be intimidating, just because there's so much you can do, but that doesn't mean you have to do it all. So yeah anyway here's what I would recommend; hope y'all have fun :D