Getting citizenship is rather easy, but knowing wether you're doing vanilla or one of the larger mods might help because some stuff might work and other might not. There are 2 general ways of getting citizenship - passing the test and doing the Gecko reactor quest. Passing the test requires very high stats (9 PER, 9 INT, and 9 LCK - you can temporarily raise PER and INT but LUCK is a lot trickier and requires a perk and a visit to NCR to get it up by 3). Doing the Gecko reactor quest is easy enough though:
Talk to Lynette (carefully, minding not to piss her off, save before hand), then go to Gecko and talk to Harold about it, then instead of Lynette, report to councilor McClure (same building, eastern wing), pick the required part up, go back to Gecko and either talk to the foreman Festus (the keycards which unlock the doors are scattered around the containers in town, but I think all 3 can be also found in the Reactor plant), or install the part yourself using the computer. I'm not sure there are any skill requirements for any of it.