Entry kab karu????

Agar ek accha share hai with the view of next 2-3 years aur mujhe ek bada amount uspe lagana hai toh how can i ensure ki mein uss stock ki lowest(close to it) price par invest karu. Kafi baar aise stocks last ek month mein 15-20 percent returns de chuke hote hai. Abhi girne ka wait karta hu toh aur badh jaate hai Aur paise daal du toh pehle kaafi girte hai fir badhte hai