There are many ways to get to Ayutthaya city from Bangkok, but I chose to use a minivan.
From what I understand, the minivans leave from one point around the circle of the Victory Monument BTS stop. Walk out exit 4 and proceed past the the exit. Take the first steps to your right (not the escalator). It is on the eastern side of the monument.
There should be a line of people waiting. Just ask and make sure. A lady (who seemed to speak absolutely no English, but understood “Ayutthaya”) then comes around and asks for payment of 60 baht for a one way trip. Everybody (Thai and foreigners) paid the same amount, so it doesn’t seem as if they’re ripping anyone off. I waited in line for about five minutes for a minivan to pull up, and another five minutes for it to fill up, before we left. The minivan was air conditioned, which made the journey of just over 90 minutes fly by.
The minivan dropped us near the downtown area on a random corner. Here tuk-tuks with “guides” were ready to pick up and show you around, but there were also a couple of shops with scooters and bikes for rent.
You can get a minivan back to Bangkok from the same spot where it dropped you. They follow the same procedures and only leave once the van is full, and again charges 60 baht per person.
Read more about Cycling in and around Ayuthhaya here.
Comment below if you have had a different experience or know of anything else worth mentioning.