[Idiom] Qestions

Hi, lets say i dont think someone's worth the time to be with.. like.. in spanish we say "dont waste gun powder hunting crows" or bad birds, like, dont waste your good things with someone who's not gonna be the same.. or something like that.. hope you could understand what kind of idiom i need.. and other one which can be very usefull as well is (in spanish is something like this: If the river sounds is because it brings rocks is something like if there's smoke theres fire.. like the one you presented here).. other one i'd like to know is like when someone gets angry its because they know that the other person is right.. in spanish is like.. if your jumpy its because you ate spice.. like hot pepper.. thats the most difficult to translate
PLEASE PLEASE i need to know which idioms come closest to these meanings.. thank you very much

[konungursvia]

Where there's smoke there's fire.

Let the galled jade wince (whoever is wrong will be uncomfortable).

Gilding a lily (putting gold on something already lovely).

These come to mind, so far...