A monitor should describe a search you would actually act on. If you would ignore most matches, make it narrower before turning it on.
Use the smallest area that still makes sense. A neighbourhood, postcode district, or named area is usually better than a whole city.
Set the real maximum you can reply to quickly. If you include listings above your comfort zone, alerts become noise.
Only include options you would genuinely view. Broad searches find more listings, but not always better matches.
Pick Office space as the property type to watch offices to let instead of homes. Office searches use Rightmove's commercial lettings; the other sites are watched for homes and rooms only. Offices have no bedrooms and no nestrrr score, so their alerts show the rent, floor space and availability for you to judge.
Use separate monitors for genuinely different searches, for example different areas or different budgets. That makes alerts easier to understand later.