Start at the nano stakes and build your way up, some might disagree, but I think thats what you need to do, unless you have been playing NL200 or something, then you can start a bit higher, but just get back on track and build up some confidence.
i'd just drop down to a level or two below what you were playing before. try and beat that over a nice sample then move back up to your normal game. or if you feel confident again after a while then why not play your old regular stakes
really depends on what you think will work for you.