It always applies ‘to yourself’. Most of those are straightforward, but sometimes the meaning changes entirely. In that case, the dictionary usually indicates it.

TL;DR : It’s historical. If there seems to be no link now, there probably was at some point.

Most of the time the link is logical. You can “adapt” something, and you can also “adapt” yourself (to a situation).

However, many words reflexive words have little to no link in meaning to their non-reflexive counterpart. My guess is it’s because the meaning slid with time, to mean something more metaphorical.

For example with “se rendre (à quelqu’un)”, it’s not hard to find the link between giving yourself back and giving up a fight, and letting yourself be captured by your enemy.

There are reflexive words where the link is pretty farfetched, but it’s still there somewhere.

As the question and accepted answer in this thread explain, there are a number of possible meanings that pronominal verbs can carry. Now I understand that you’re wondering how you can map a given verb to its pronominal meaning. Short answer: there’s no failsafe way to do so. Ultimately, you have to learn pronominal verbs via their own dictionary entries to verify the meaning. On the fly, however, here are the strategies I usually use, before “polishing” the result. Mileage may vary.

1. See if the transitive meaning can be understood reflexively.

« Je me vois dans le miroir. »

→ Voir : to see

→ Guesses for se voir : to see oneself

→ Best guess: “I see myself”

2. If context forbids, see if the transitive meaning can be understood reciprocally.

« Ils se voient tous les trois jours. »

→ Guesses for se voir : to see oneself ; to see each other

→ Best guess: “They see each other”

3. If context still forbids, see if the verb makes sense with a passive or “verb-able” meaning.

« Le soleil se voit à travers les nuages. »

→ Guesses for se voir : to see oneself ; to see each other ; to be seen ; to be visible

→ Best guess: “The sun is seen” or “The sun is visible” depending on context

Now we’re through with the “literal” meanings (those whose translations can be explained word for word). The reason I started with them is that I’d say one of the above will work for the majority of verbs that are transitive in both English and French — and for that reason they won’t all be listed in dictionaries, because they can be deduced in a straightforward way from the non-pronominal verb.

After that, you start to allow more tolerance of figurative meanings.

4. Try a reflexive meaning that maps most naturally to a non-reflexive verb in English. Might be particularly common for verbs indicating movement.

« Je me couche à 21h chaque nuit. »

→ Coucher : to sleep ; to spend the night ; to lay down ; to put to bed

→ Guesses for se coucher : to lay oneself down ; to put oneself to bed

→ Best guess: “I lie down” or “I go to bed” depending on context

Other examples: s’asseoir, se lever, se diriger

5. Or a passive meaning that maps most naturally to a non-passive verb in English. I find this is often viable for verbs communicating an emotional state.

« Je me fâche. »

→ Fâcher : to anger, to vex

→ Guesses for se fâcher : to anger oneself ; to anger each other ; to be angered

→ Best guess: “I’m angered” → “I become angry”

Other examples: s’irriter, s’étonner

6. After exhausting those options, you can tentatively try to simply delete the pronoun in translation. I think this works pretty well when the subject is in some way affected by the verb, and/or the verb is followed by de.

« Je me moque de lui. »

→ Moquer : to mock (literary only, but a good start because of the English cognate)

→ Guesses for se moquer : to mock oneself ; to mock each other ; to be mocked ; to mock

→ Best guess: “I mock” (in theory we could have wrongly guessed “I’m mocked by him”, considering Je m’étonne de lui, but hopefully context would rule it out)

Other examples: s’échapper, s’apercevoir, se méfier

7. Finally, when neither changing the verb along one of these lines nor deleting the pronoun yields any sense, you have to resort to using a dictionary.

« Elle se bat. »

→ Battre : to beat ; to defeat

→ Guesses for se battre : to beat oneself ; to beat each other ; to be beaten ; to beat

→ The context is likely to rule out all of the above, given the dictionary meaning: “She fights”

Other examples: s’agir de, se débrouiller

So that’s more or less the process I’d use. If none of them worked, I’d allow a little more figurativeness to work into my guesses. (For example, « Ça se voit » : “It shows” rather than “It’s visible”.)

And at the end of the day, I’d still check in a dictionary. I mostly use the above strategies if I’m reading a book and don’t want to keep pausing to look things up. Otherwise the dictionary is probably faster. 🙂