Solar noon is 12:00 plus 4 minutes for every degree of longitude west of the middle of your time zone, plus or minus up to 16 minutes through the year, plus an hour in summer time.
The Earth turns 1° in 4 minutes, so a place 1° west of the meridian its clock is set for sees the sun cross the meridian 4 minutes later. On top of that the equation of time (the tilt of the axis and the ellipse of the orbit) moves solar noon between about 16 minutes early (in early November) and 14 minutes late (in mid-February) through the year, and daylight saving shifts the clocks, not the sun, by an hour. London, almost on its meridian, has solar noon at 11:44 at the start of November and 12:14 in mid-February (GMT).
It treats a time zone as a straight strip. Zones are drawn for politics, so a place can sit many degrees from the meridian (Madrid in summer, with solar noon after two in the afternoon, and western China are the famous cases) and the same rule then applies with a much larger first term. The equation of time varies slightly from year to year in its dates, and the sign of the longitude term depends on being east or west of the zone’s meridian.
Estimate with the rule, then check it against the calculator that models it properly.
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