The Minister (Tian Xiang, 天相) in the Self palace (Ming Gong, 命宫)

What the classic says, Zi Wei Dou Shu Quan Shu (紫微斗数全书), volume two

The seal (化印), and a ruler of office. Shining on the self or the body palace, honoured; as the ruling star it makes a person exacting with themselves, and with the Wealth palace (财帛) and the Career palace (官禄) palaces strong the household prospers. With the Iron (武曲) and the Disruptor (破军) together, and the Blade, Millstone, Flare and Ember (羊陀火铃) as well, worse — a craft or a trade, or peace found in religion.

天相水，南斗化印，为官禄主。天相入男命吉凶诀：天相星辰贵等伦，照守身命喜无垠，为官必主居元宰，三合相逢福不轻。天相吉星为命主，必定斯人多克己，财官禄主旺家资，权压当时谁不美。天相之星武破同，羊陀火铃更为凶，或作技术经商辈，若在空门享福隆。天相入限吉凶诀：天相之星敢主财，照临二限悉无灾，动作谋为皆遂意，悠游享福自然来。天相之星有几般，三方不喜恶星缠，羊陀空劫重相会，口舌官灾祸亦连。

The classic also has lines on a woman’s chart, reading a life by its sex; they are left out here, in the Chinese as well as the English. The source link has the full text.

“Well placed” and “badly placed” refer to the star’s brightness in the branch the palace falls on: the same star in the same palace reads differently bright and dim, and the clause says how.

Source

How this placement actually turns up

• Well placed (exalted or strong) in 41% of those charts, badly placed (fallen) in 16%, in between the rest.
• Alone in the palace in 50%; sharing it with The Mystic (廉贞) 18%, The Emperor (紫微) 17%, The Iron (武曲) 15%.
• How often the conditions the classic’s line names actually occur — one of the four difficult stars (擎羊陀罗火星铃星) in the palace with it: 32%; Earth Void or Earth Robbery (地空地劫) with it: 15%; Lu Cun (禄存) with it: 9%.

Counted by casting every day from 1950 to 2009 at each of the twelve hours — 262,980 charts, 8.3% of which have The Minister here (every main star sits in every palace in about one chart in twelve). A count, not a reading.