The main thing he did was watch over Luke. That was his main purpose there, as he said to Bail Organa and Yoda on Polis Massa. Yoda says "To Tatooine, to his family, take him.", and Obi-Wan says "I will take the boy and watch over him." There are many instances in the legends where he 'saves' Luke from skirmishes, etc. even though Luke's Uncle Owen wasn't too happy about that.
With regards to his own life, he continued with his training, despite not having a master with him. As Yoda says to Obi-Wan on Polis Massa, Obi-Wan's old master Qui-Gon had contacted him and had found the way to 'come back' to the world of the living and interact with people. Qui-Gon had not completed his own training, so he could only come back as a voice (I think), but he told Yoda how to do it. Yoda taught Obi-Wan, and he spent at least some time on Tatooine training with this particular 'power'.
This last part is just speculation, but he might also have travelled at least around the immediate vicinity of where he lived and where Luke lived, and got to know a bit more about the planet he was on. Evidenced by:
- He knew a deal more about Sand People than Luke, though Luke had been living there as long as Obi-Wan. When Obi-Wan and Luke found the butchered bodies of the Jawas who found C-3PO and R2-D2, Luke suggested it might have been the Sand People who attacked them. But Obi-Wan says that the blaster marks on the Sandcrawler were too accurate for Sand People, and guessed correctly that it had been Imperial Troopers who killed the Jawas. He probably interacted with the Sand People enough to know how well they shot. When he saved Luke from them, he also knew how to scare them off.
- He was familiar with the denizens of Mos Eisley. While Luke did mention the town in the movie, when they actually went there, it was Obi-Wan who somehow knew exactly how and where to find a smuggler. If he'd simply found a passenger ship, this could be waved off. I'm sure many people would want to leave Tatooine, and would not need to do it so hush-hush, so a simple cruise ship would be what most travellers look for. But Obi-Wan found a smuggler of all things, and normal people who are unfamiliar with the place would not be able to find one that easily.
- He also knew Chewbacca. While in Episode 3, we see that Chewbacca formerly knew Yoda and helped him escape Kashyyyk after nearly being killed, we also see that Chewie remained on the planet, and did not follow Yoda to Polis Massa. So, since that is the only moment before Episode 4 where Chewie appears, and he does not meet Obi-Wan then, it only makes sense that Obi-Wan only met Chewie after he started living on Tatooine.
EDIT: From the wiki, the cantina on Mos Eisley was indeed a popular gathering place for spacers, smugglers, and the centre of a host of criminal activity in Mos Eisley. So you could argue that Obi-Wan might have simply heard about the place, brought Luke there, and met Chewbacca by chance. But to have asked around for smugglers who were willing to evade Imperial Troopers would have attracted too many unwanted questions and rumours. There was a very high chance that some smuggler could have rejected them, and then tattled to the Imperials for money, if Obi-Wan had simply walked in without a plan. In fact, someone did tattle to the Troopers just before the Millennium Falcon took off.