I am going to speak to those who are coming from the North or West of town. There are 2 primary options for where to park your car. Alewife station on the red line, and Riverside on the green line. These are both the final stop on these lines, so from there you only have one way to go, which is inbound. This is nice if you are totally clueless, because it eliminates the possibility that you hop on the train going the wrong way. Alewife has over 2,000 parking spots and Riverside has about 1,000. The key difference is that Fenway is on the green line, which means from Alewife you would ride in on the red line and then at the Park stop you would get off and get on a green line train headed toward Kenmore. Although I have heard you can just follow the crowd, I didn't even want to mess with that.
Therefore, I drove a little further and went to Riverside. This was right off of interstate 95 and couldn't be easier to find off the exit. Plug the address into your GPS and you can't miss it. I also liked how the parking lot was a big open air space and not a garage (pictured above). I arrived at 5 PM for a 7:10 game, which I would recommend. There were hundreds of open spots at this time, and you pay $6 when you arrive and take the spot of your choice.
I mentioned that this is the final stop on the green line, so I liked the fool proof element that I could get on any train and they were all headed to Fenway. By being early, the crowd was really light but there were certainly people in Red Sox gear getting on board with me. There are kiosks where you can purchase a ticket or card, and in this case they had people from the MTA standing there to help out and make things go quicker. Although my only intention was to ride the train to the game and back, I got a Charlie Card and loaded it with $4.00. This is a little plastic card that most local people have, which you can just reload with more money. The one key advantage is that rides were only $2 with this card and $2.50 if you bought a traditional ticket. I certainly did the right thing here because I could just get right back on the train to come back rather than stand in line to pay for another ticket. To get in the gates, you just hold the Charlie Card in front of a little black box and it reads it and lets you in. There is no swiping or inserting the card - just wave it and move on. You'll notice a lot of people already have the card in their wallet and just hold there wallet up in front of the card reader. If you want to feel really cool - do that.
I hoped on the train to Fenway, and the crowd was very light. I had a seat on the train and though we picked up more people as we got closer it never got close to full. This was really relaxing and let you get a glimpse of some different neighborhoods. I felt as safe and secure as in my mother's arms. When you are from out of town I know safety is a concern, because you don't know about the different parts of town. However, there were a lot of families on the train and it was a pleasant experience. There are 2 stops where people will get off, 1 is Fenway and 1 is Kenmore. I got off at Fenway which is the first of those 2 stops you come to from Riverside. Most people going to the game seemed to do the same. There were clear signs pointing you in the direction of the ballpark (see below) and they lead you out to the main road where it becomes impossible to get lost.
Getting off at Fenway worked well, and I was about a 5 minute walk to the park. I would say between the ride in and the walk to the ballpark it took about 45 minutes from when I parked. Given how stress-free and simple it was, I was thrilled that I didn't drive in close to the ballpark. Another thing worth noting is that the walk from Fenway station puts you at the 'cool' entrance, right behind home plate. This is the famous exterior picture you've seen of the ballpark and where most of the pre-game buzz is happening.
After the game (I left in the bottom of the 8th with the Sox up 6 - 1) I went back to the same place. Again, it was easy to follow the crowd back to the station, although I could have found it myself by retracing my steps from when I arrived. Because I prepaid for a second trip on my Charlie card, I was able to bypass a big line of people paying cash and walk through where an MTA worker had a portable scanner just for us smart people with a pre-loaded card.
I heard that the ride back could be much more crowded, and it was. However, even this wasn't as bad as I thought. It was a Monday night, but the game was sold out and a bunch of people were leaving when I did. At worst case you may have to let a few full trains go by before you can find some space. However, plan on being crowded for a little bit headed back. My view below: