There are various methods for auspicious date selection had been passed on from china ancient time to nowadays. Some popular and commonly used ones by  chinese feng shui and fortune telling practitioners are, such as bazi 4 pillars四柱, dong gong董公, zi bai flyingstar紫白, sam he nayin三合纳音, xuan kong dagua 玄空大卦methods, etc. Some may use just the chinese almanac book "tong sheng 通勝 (tong shu通書)"  for simplication.
 
A very famous top ranked feng shui master Mr Chan Pui Sang （1924-2014）, the founder of his Miao lineage(妙派) of the Sam Yuan Xuan Kong DaGua （三元玄空大卦派）stream, passed away last year.  Master Chan had also mastered the Sam He feng shui science since young .
 
The old master Chan ever said, in sam he science,  where the auspicious date selection method is very concerns about the relationship on nayin elements between the client's (yin or yang mansion master) birth year pillar and the selected date day pillar. Only the selected day pillar nayin element produces生 (give birth) or make strong旺 the client's birth year pillar nayin, then would be considered as auspicious date for recommendation.
 
Those selected dates'  day pillar nayin element:  
  • produce the client's birth year pillar nayin element, is named "birth qi" day
  • control (kill) the client's birth year pillar naiyin element, is named "killing qi" day
  • being produced by the client's birth year pillar nayin element, is named "retreat qi (drawback, exhausive) day
  • being controlled (killed) by the client's birth year pillar nayin element, is named "wealth qi" day
  • is the same as the client's birth year pillar nayin element, is named "strong qi" (prosperty) day
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三合擇日法 - 日干支納音五行與命五行的關係
巳故香港妙派大師 陳倍生 先生曾有説：福主出生年之干支, 即出生年太歲的干支, 其納音五行, 與擇日干支之納音五行, 關係很重要, 必需得日的生旺, 才算好日子。 
凡是,  
生命者叫生氣日。 
剋命者叫煞日。  
命生日者叫退氣日。 
命剋日者叫財日。 
日與命五行相同者叫旺氣日。