AND = "A" when there is any type of contradictory between both parts:

• "I love you and you love him" - "Ja kocham ciebie a ty (kochasz) jego."
• "He cooks and she cleans the house" - "On gotuje a ona sprząta dom"
• "She is young and he is old" - "Ona jest młoda a on (jest) stary." (In the phrases containing contradiction, the repeated verb can be omitted). BUT: {@style=color: red} if the contradiction is not real, you only use different words to describe similar state, you go into nuances: "He is old and she is also not quite young" - "On jest stary a ona też niemłoda" (there is however some age difference between them, so she is younger than him) or "On jest stary i ona też niemłoda" (they are pretty similar, only you want to be polite and do not use the word "old" to describe a woman).
• "Her blouse is white and her skirt is red" - "Jej bluzka jest biała a jej spódnica (jest) czerwona." - it is so when the used verb is concerns the clothes itself, not the person who wears them; It works the same for longer lists: "Her hat is blue, her blouse is white, her skirt is red and her shoes are black" - "Jej kapelusz jest niebieski, bluzka biała, spódnica czerwona a buty czarne." see also below {@style=color: red}

AND = "I" when there is clear connection or similarity of both parts:

• "I love you and you love me" - "Ja kocham ciebie i ty kochasz mnie." (Attention, in this very case it would be also correct "Ja kocham ciebie a ty mnie", to underline sort of dualism: "you"-"me", while usage of i underlines the mutual similarity. With the usage of a, the repeated verb should be omitted).
• "He cooks and she cooks, too" - "On gotuje i ona też." or "On gotuje i ona też gotuje." or "On gotuje i ona gotuje."
• "She is young and he is young" - "Ona jest młoda i on jest młody."
• "Her blouse is white and her skirt is white" - "Jej bluzka jest biała i jej spódnica jest biała." or "Jej bluzka jest biała i jej spódnica też."
• BUT: {@style=color: red} when you enumerate the parts of clothing that somebody wears i.e. it is about the person, and not about the clothes, you rather use i no matter, whether they are similar or different (as there is no contradictory within the person itself, and the verb relates to the person, not the clothing): "She wears a white blouse and a white skirt" - "Ona nosi białą bluzkę i białą spódnicę."; "She wears a white blouse and a red skirt" - "Ona nosi białą bluzkę i czerwoną spódnicę."

It's natural.

"i" connects accompanying occurrences, happening somewhat one beside the other

"a" connects occurrences in some logical sequence