I'm posting before the cadre of players telling you to lern2play and saying "NICE KNOWING YOU, GOOD TO SEE CASUALS BAWWING CUZ HUR DUR LEVELZ WER HANDED OUT ON A STICK" (Edit: Aw, I just missed it before the troll above me posted). I'm sorry to see you leave. Since it's only a few days into the patch, I think it's best to see what Square's response will be to the difficulty increase for those who are soloing/lowmanning. It is generally suggested to go after monsters at or below your level now - anything higher than you does require a "skilled" party (usually composed of players that already multiclassed and have skills from other classes to enhance their survivability).

There was another thread that gave good tips for lower level players: you will probably have to multiclass to get some healing skills. Pugilist, Thaumaturge, and Conjurer all provide healing skills that will extend your longevity and make things easier to handle. But yeah, at most go after stuff that's one level above you, but I'd generally just go after stuff exactly your level to make things easier.