There are no settings that you can fall back on that will work every time (except maybe the
Sunny 16 Rule); photography simply doesn't work that way. Each shot will be, practically speaking, unique; and you, as the photographer, have to learn to adjust for those changing conditions.
To get a better grip on learning to shoot in Manual more intuitively I suggest you pick an aperture you think will work and give you the depth of field you want, say for instance f8. Set your camera to use that aperture manually.
Switch to "A"perture Priority mode, meter the shot and take note of the suggested shutter speed.
Switch back to "M"anual mode and enter the suggested shutter speed.
Now take the shot and see what you think. Based on that shot, either use reciprocity to adjust your exposure (e.g. f8 at 1/125s = f5.6 at 1/250s = f11 @ 1/60s, etc.) or use the Exposure Compensation button to get the shot you're after.
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