Okay, the start of this method also is the same as a method of picking up girls, but the conversations and topics are very different after the introductions.
First, we'll start with location. This method is for standard bars like The Hub and not Izakayas (there is a way to meet people at Izakayas, but it's a bit different and more difficult)
Second, get a good seat where you can watch everyone who comes in and out of the bar.
Third (this is where it gets different that the same style for picking up girls), look for tables with an even number of guys to girls or more guys that girls. The reason is simple: it is to make yourself seem as intimidating as possible.
Fourth, grab a new drink and swing by their table on the way back to your table. Open with a "Kanpai" by holding your glass up and getting a cheers back. If they go for it and don't seem too "WTF are you doing?" then start up a conversation. This is a really good chance to practice your Japanese as they will more than likely speak no English. Open with a "What do you do?" or if they are young, ask "Are y'all students?" and start up a conversation by using as much Japanese as you know. Ask what they are drinking and tell them more about yourself. Try and sit with them and drink as long as you can. By the end, you should have a new group of friends to hang out with the next time you go out.
I wish you luck! Be friendly, never embarrassed and always smile.
Thanks for reading,