This is a log of bugs and errors I faced in coding my Arduino project:

-High voltage current handling: the switch of a 12v pump can get tricky to handle as you need to involve a power source and always be sure in case of the current falling back, the switch will be there and handle it.
-LCD soldering: I encountered different errors when i finished soldering the lcd, the real problem with it is that it has so many pins that you have to understand wether is the character pins which is faulty or the line controller. 
-Water level sensor keeps giving wrong values, doesnt matter the resistor involved or if the value is mapped, it also get mud on the modue itself which is not safe for the plant and for the whole circuite.
-Wires are really messy, I know I'm not a tidy person at all but they drove me crazy, no matter my trials to keep them separated and more easily understandable..