Lightbulbing works the best when you can trade the bulbed tech to everyone else and that way get many techs instead of one. Otherwise I usually see no reason for bulbing anything. A few exceptions are of course possible, like getting a religion (Christianity/Taoism/Islam). Settling is always a good option, and this is what I usually do if I don't have anything else in mind.
Some people never settle Great Artists, because they don't like those and don't want more of those. I don't love GArtists either, but they aren't completely waste. A city under heavy culture pressure can be culture "bombed" by "creating a great work", or the artist can be settled to get more culture in the future. And the little gold bonus the artist gives is nice too. With Great Engineer you can hurry production of a building. This way you can complete wonder in one turn, if you want to secure it fast. GEngineer works good when settled too. Great Prophets can be used for building shrines for religions in holy cities. This is good source of money if your religion has spread a lot. But if you don't have a holy city or if your religion has spread just to few cities, it's not always the best option to build the shrine. Settling may do a better job in that case. Great Spys can infiltrate enemy cities and that way give you a lot of Espionage Points. With those points you can for example steal many techs from your enemy, or support a city revolt to bring down the cultural defence for one turn. If you decide not to use your GSpy for infiltrating, you need to decide between settling and building scotland yard. Which one is better depends on how many EPs you are producing at the moment and how much you will produce in the future. Settled GSpy also gives few beakers. Great Scientists can build academies in your best science cities. In early game this usually is your capital. Settled GScientist gives you good amount of beakers, especially in the early game and under representation. Great Merchants can do a trade mission in foreign city. This will give you a huge amount of money if the city is big enough and far from your capital. Settled GMerchant gives good money, which can help a lot too.
Golden Ages can be very powerful too. Usually if you get a Great Person you don't want, you use it for golden age. Many players use the Great Artist from Music for GAge. Golden ages are more attractive, if you built The Mausoleom of Mausollos wonder. But saving 4+ GPs for next Golden Age is huge waste from my opinion.
Using your GPs for corporations may be good option too, but saving a GM for 1000 years just to get Sid's Sushi isn't really good decision, I think.
Remember, everything is situational

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