Well, there are several methods. The safest is to quit the game and wait. Your persona will get back about one point of stamina for every minute you don't play with it. Either use another persona instead, potter about in the Library, or log off and save money!

A similar way to get back stamina safely is to stand around in the Tearoom when you enter the game. This is quicker than leaving your persona out of play, but of course you will be paying money while you wait. Quite often when you enter the game there will be people hanging around in the Tearoom recovering lost stamina, and they will usually be only too pleased to have someone to chat to; if you need any help or advice, or just a shoulder to cry on, just sit around in the Tearoom accosting people as they enter!

A more dangerous way to regain stamina it is to SLEEP. Here, you get your stamina back at the rate of 1 every 2 seconds after the first 6. If you are attacked while asleep, however, the consequences with respect to your health will be severe! It is also difficult to sleep sometimes because other players keep making noises and waking you up (but not always in bedrooms).The quickest way to regain stamina is to eat a wafer. These are highly sought-after objects found in places which are difficult to get to, but they will immediately add an amount to your stamina if you eat them. As with treasure, there are some wafers which are intended expressly for the use of low-ranking players, especially in the monastery area.

Of course, there are other ways to get back stamina (eg. certain potions and spells), but they're not all that important to low-level players such as yourself...