Such things as calling a stranger in the street, addressing somebody in a shop and attempts to draw a waiter`s attention in the cafe have been a real torture for us (Russians) for the last couple of decades.

But there are some rules that anyone can follow if one finds himself in such a situation:

1.A boy or girl can be addressed мАльчик (mAl`cheek - boy) and девочка (dyEvachka - girl).

2. A person looking between about 14 (a teenager) and 35 could be addressed as молодОй человЕк (maladOy chelovyEk - literally, a young man) or дЕвушка (dyEvooshka - a girl) though sometimes it can be quite difficult to make any reasonable age boundaries.

3. The problem is that there are currently no universally accepted proper addressing to older people in the modern language. Though a child before about 8 can call an adult дЯдя (dyAdya - literally, uncle) / тЁтя (tyOtya - literally, aunt) or бАбушка (bAbushka - literally, grandma) / дЕдушка (dyEdushka - grandpa). The latter are also appropriate for younger people to address senior people, but only if they called them сынОк, дОчка, внучЁк or внУчка first even though they don`t have any family connections.

"Эй!" ("Hey!") interjection is often used when addressing people though it can seem a bit rude.

Besides, there are several addressings of limited use:

гражданИн (grazhdaneEn - literally, citizen (male)) / граждАнка (grazhdAnka - citizen (female)) (often used by law enforcers, also may be used by strangers but, in my opinion, this sounds too official or hillarious like shown in this videoclip from a very good Soviet comedy "ДжентльмЕны удАчи" (literally, "Gentlemen of good luck"))

https://www.youtube.com/watch?v=Be1ZHRri78I

товАрищ ( tavArishch - comrade, or mate) (widely used in Soviet times but almost extinct now, though still acceptable. Without adding a surname, only appropriate for males.)

мужчИна / жЕнщина (are only appropriate to draw attention of a complete stranger you're unlikely to ever talk to again, in an urgent case).

МужчИна, вы кошелЁк уронИли. (Mooshcheena, vy kashyelyOk ooraneElee - Man, you have dropped (your) wallet)

ЖЕнщина, вы выхОдите на слЕдующей останОвке? (on a bus, for example) (ZhyEnshcheena, vy vyhOdeetye na slyEdooshchcey astanOvkye? - literally, Woman, are you getting off at the next stop?)

уважАемый / уважАемая can be used (somewhat ironically) to make a polite remark to a person violating the norms of behavior:

УважАемый (male) (Dear or Honourable), разрешите пройти. (OovazhAyemyi, mozhna praytee? - literally, Dear, can I get by?)

УважАемая (female) (Dear or Honourable, literally respected), уберите тележку. (OovazhAyemaya, push aside a trolley)

If in doubt, it would be best to use an impersonal addressing: прошУ прощЕния (prashoO prashchyEneeya - Excuse me (informal), извинИте (IzveeneEtye - Excuse me, more formal way) etc