I'm not new to Persona, but i'm new to SMT. play persona 3:FES (this is a better, improved version of the original, or play portable for the chance to play a girl and get a male harem :^) ) next, then 4. then play the persona 2 duology (in order- innocent sin, then eternal punishment) play persona: revelations (the first one). if you really like persona, play the arena spin-offs (i dont really recommend them, or Dancing all night. bleh.) I haven't played persona Q, but i heard the battle system is good in that one.
as for SMT, people say to play SMT IV first. i'm going to buy nocturne and digital devil saga soon, to which there is a sequel. then devil summoner, which also has a sequel... there's also devil survivor (so many demons). also has a sequel. i think those are all the notable SMT series. if you have any more questions ask me kek