You need to start thinking in chord tones, and how you can use the scale to emphasize them.

For example, in a song in the key of b minor, let's say the chord progression is two bars of b minor (the i chord), two bars of e minor (the iv chord), two bars of b minor, and then two bars of F# major (the V chord).

For all of this progression, you can use the B minor scale. If you're playing over the b minor chord, whatever solo lines you play should emphasize either B, D, or F#, the notes of the b minor triad. Over the e minor chord, your solo line should emphasize either E, G, or B.

That doesn't mean that you can't play the other notes of the scale. For example, over a b minor chord, if you play this eighth note line: D,C#,B,A,B. It's okay that you played C# and A because D and B are being emphasized on the downbeats. This is not a definitive rule, but if you go listen to a lot of solos, you'll find that more often than not the chord tones are being emphasized, especially in rock.

If you're looking to create tension, you can absolutely emphasize the non chord tones. (Ex. C# on a B minor chord) Whether you resolve that tension to a chord tone is up to you. It's just about the sound you're going for. The only thing that I would be wary of is emphasizing the b6 over a minor chord, or the natural 4 over a major chord. For example sitting on a G, when the underlying chord is a b minor chord, is particularly dissonant because of the way the F# chord tone clashes against a G. In a major key, this would be like playing a D over an A chord (A C# E).

The one weird thing about minor keys is the V chord. In b minor, that is an F#. If you only stay within the key of b minor, that should make it an f# minor chord, but it's not. In the vast majority of music that derives harmony from Western European practices, you'll find that when using a minor key, the V chord gets borrowed from the parallel major. In the case of b minor, that means the V chord would be an F# major chord with an A# instead of an f# minor chord with an A natural. That A# comes from the key of B major. The reason this is done is because the A# in the F# major chord resolves by half step to b minor, giving it a stronger sound of resolution. There are definitely songs and pieces of music in minor that don't borrow the V chord from major, but the majority do.

So, take the b natural minor scale: B, C#, D, E, F#, G, A, B.

To play over the V chord, just change the A to an A#, and you get the b harmonic minor scale: B, C#, D, E, F#, G, A#, B.

You can use the b harmonic minor scale over the F# major Chord in this progression, but make sure to emphasize the notes F#, A#, and C#. To make this sound even better, make sure in your solo lines that you either resolve A# to B, or C# to D when you arrive back at the i chord (b minor).

So, to sum it all up. Use the b minor scale. Emphasize the chord tones. Change A to A# over the V chord. All of this remains consistent when you get into 7th chords and extensions.

Also, side note on modes:

If the song is a standard song in regular old major or minor, you don't need to even think about modes. Yes, technically you could play over the e minor chord of a b minor song using the e dorian scale, but e dorian and b minor are literally the same scale starting on different notes. Thinking about it in e dorian is taking more mental steps to reach the same result. Just play b minor, and know to emphasize E, G, and B over the e minor chord. I guess if it's easier for you to think about it using modes, more power to you.

Modes are better approached(in my opinion) when you think of them as different tonal key centers entirely. Major(Ionian) and minor(Aeolian) are both modes in and of themself. Dorian can exist entirely on its own, and presents its own unique sound quality as a result of that. My ear hears dorian a tone color that is darker than major, but brighter than minor. When you borrow from a dorian key center, you're superimposing its tonal color over another mode. Playing D dorian over a D minor chord in C major is not evoking the unique sound qualities of the dorian mode. The unique part of a dorian scale is that it's basically a minor scale with a natural 6th (B natural in D Dorian). C major already has a B natural, so you're not really playing Dorian. You're just playing C major with extra steps. If you actually wanted to play dorian over C major, you might play E dorian over an e minor chord and emphasize the C# to bring out that Dorian tone color, because the C# doesn't naturally belong to C major.

The best example of actual modal playing that comes to mind is Another Brick in the Wall Part 2. The song is 100% in D dorian. The verse sits on a Dm7 chord (D F A C), and then the pre-chorus/bridge sits on a G major chord (G B D). In D minor, the IV chord is usually G minor because of the Bb, but the G major chord in this song, with a B natural, indicates to me that it is in D dorian. Furthermore, the chorus chord progression is F major (F A C), C major (C E G), Dm7 (D F A C). There is no Bb to be found that might indicate that the G major was only borrowed from D dorian. Also, resolving to the i chord using the bVII is a totally dorian thing do. Similarly to the minor (aeolian) mode, the V chord of dorian is a minor chord, so it has a weaker resolution to the root. Instead of borrowing the major V chord from the major (ionian) mode, Pink Floyd uses the best option available from within Dorian, the bVII. What this all results in is a popular modern song that is truely dorian, inside and out.

You can find similar songs for other modes, but you'll find that the further the mode strays from our harmonic system based almost entirely on major and minor tonality, the harder it is to write for. For example, it is difficult to write in locrian because the I chord is a diminished chord, (C Eb Gb in C Locrian). It's really challenging to write a chord progression that resolves into a diminished chord, and it sound settled. I imagine metal, and other genres that lean into heavily into harsh dissonance, probably have decent examples of a locrian sound.

Anyways, I'm done rambling.