"Profit" is a relative term. With only one 55g tank, the best you can hope for pay your expenses plus maybe a few extra dollars.
You'll want some decent light, some good co2, and a nutrient rich substrate. After that you'll want to grow some more rare/difficult plants. Those are they only ones that are remotely "profitable". The easy plants or the ones that grow quickly don't sell for a lot of money, and therefore won't "profit"
Most of the people that you see selling plants en masse generally buy them wholesale and resell them online at retail. Most of us hobbyist don't really make money, we just cover our expenses. To come out ahead, you'll need more than a 55g.
you have done this before??? if so what size tank and what plant and what parameters?????