2) Navigating between the different party atmospheres...
Generally speaking, the norther you go, the more prostitutes and the more drugs you will find. Many Jakartans never venture in North Jakarta because it has a very bad reputation and it is considered as dangerous. It is partially true: In this area, you will see that people outside the clubs are more annoying and aggressive. They will try to get money from you one way or another, asking you the more often for parking money (they make sure nothing happens to your car while you park) and taxi money (they stop the taxi for you. Very annoying because you can do it yourself. Avoid that by walking away a few 100 meters, otherwise pay something like rp2000). In the north, you also have to be very careful with taxis. You will discover many taxis' names you had never heard before, and most of them try to copy the appearance of the trusted Blue Bird or Express. When I can, I always try not to catch a taxi right outside a club, and prefer to walk until a larger road, where i will take a Blue Bird or an Express. I don't think it's so dangerous, but I don't like being in the car of someone I don't trust. Apart from that, the reputation of Kota as a dangerous area in Jakarta is a bit overexaggerated, especially if you compare it to the dangerous areas in western countries, where you would never walk alone.
Clubs in North Jakarta ALWAYS have prostitutes (except Churchill Bar and maybe K7), usually a combination of freelance prostitutes and girls under contracts. It has to be the biggest red light district in the world, and contrary to western belief, prostitution in Indonesia is not imported by sexual tourism, it is a very common practice among Indonesian of all classes. In only a few clubs in Kota you might meet some"normal girls": Stadium, K7 and maybe Mille's on sunday mornings. The crowd there is mostly male, with some clubs more chinese-oriented (Sun City, Club 36), some mostly Indonesian (Mille's) or both. Once again, apart from Stadium, very very few foreigners go there and you will probably be the only bule. Kota has literally hundreds of clubs, and it's impossible to check all of them. The first time you go there, you hallucinate because, after all, you thought you were in the biggest muslim country on earth and you discover a place most terrorists would have traded there 72 virgins for. And I forgot to talk about Jakarta's underground casinos, huge but difficult to find for a cheap foreigner like me... Some clubs are incredibly luxurious (Alexis hotel, Sun City) and other are so trashy you are scared to death when inside (the Palme d'Or goes to Monggo Mas Club). Overall, you go from surprises to surprises and you never get tired... That's why I love going there..
Drugs, mostly ecstasy, crystal-metamphetamine (shabu-shabu, called yaba in Thailand) and heroin (putau in Indonesian) are very common in Kota, to a point you cannot even begin to comprehend. In some clubs, everyone is on pills, for instance in Sydney 2000. It's really scaring.. Some says that it's so popular because alcohol is forbidden in the muslim religion but there's nothing about taking drugs. I'm not sure it's true.
South of Monas, you have many more decent places, though not only. In Blok M, you have another small red light district, but oriented for expats and sex tourists. 99% of the girls there are prostitutes, working their ways to your wallet (the best way being making you there boyfriends). Personally I never go there and I don't really like it except if I'm really drunk. Hotel bars, especially the Triade BATS-CJ-Tiga Puluh are definitely pick-up joints with 85% of the girls working as freelance prostitutes. But you can also go there to enjoy the live band, music and meet other expats (male expats mostly). Girls in these places are usually smarter and better educated than other girls in Blok M but that just means they will know better how to scam you. BE CAREFUL! Cheating rate is 99%! Red Square is in between, with, I would guess, half the girls freelance prostitutes usually found in the hotel bars mentionned above.
Ok, now we've seen all the "bad" places... Since you are a normal being, you probably want to meet some normal people to and engage in healthy relationship with them. In the south, you change of atmosphere very fast... most of the best clubs are very poshy, even compared to western standards.. The most famous clubs are Dragonfly, Blowfish, Immigrant and X2. Every month or so, a new club open for socialites, models and expats, but the competition is tough on this segment and most of them fail. You also have good and popular clubs in Kemang, but they target mostly young people, mainly college and high-school students, between 18 and less than 25. In all those places, people dress well, and though you will meet many "kept" woman, no prostitutes... but of course it will be more difficult to seduce someone... Don't be too pushy, and just try to get a phone number, it's worth to be patient..
And then there are more thematic areas: Jalan Jaksa is where most backpakers party, as well as many English teachers. Mistere is the place where people go to dance salsa. Parkit Deja Vu is for heavy metal fans, BBs is for Reggae, etc.. You also have many lounges and café where it's just nice to have a drink and meet friends, lots of places with live music, thousands of karaokes... It will take you years before getting bored of the nightlife in Jakarta if you have the courage to explore it a little... Enjoy aja!