Hey fans making first trip - congrats and have a ball! I am a long time season ticket holder who has actually given up tailgating and started spending my pre-games at Patriot Place, usually Skip Jacks, where I can enjoy several glasses of wine, a good meal and not freeze my butt off along with other merry Pats fans. Skip Jacks is a kind of pricy mostly seafood place, but I have never been shut out of a table there and you can wait around the crowded bar watching the early game or pregame coverage on their many t.v.'s before your table is ready. There is also Red Robin where I enjoyed the bar but didn't get a table in time the one time I tried it. CBS Scene is always a 2-3 hr. wait by the time I get there (2-3 hours before the game) so I have never tried that one. There are several other restaurants but I usually stick with Skip Jacks.
I come from southern NH. Normally it takes me one hour and ten minutes to drive to Foxboro but I make sure I leave about 3 1/2 to 4 hours prior to kickoff on game day; maybe longer if it is a Monday night game and you have to deal with regular traffic on top of game traffic. I come down Rte. 1 South, where you will come too if you are driving from Boston or points north and I like to park in the lots just north of the stadium (between a liquor store and a Ford dealer) on the other side (from the stadium) of Rte. 1. The Stadium will be on your left, these two lots are on the right. You have to make a left to get out after the game but usually they have a cop there letting people out periodically so it goes relatively fast, most of the time (traffic and getting out after the game are often two of the biggest headaches of a trip to Foxboro. Try to relax and just enjoy the game itself). The lots, which are official stadium lots, cost $50.00 last year, and I expect it will be the same this year. There are similar lots on the other side of the stadium if you come in on Rte. 1 north. As long as you are not meeting someone for tailgating and don't mind a bit of a walk, I do not recommend parking right at the stadium. You can get trapped for hours after the game (which can also happen to you periodically in an outlying lot, despite your best efforts). Lots of tailgating occurs in every lot, so you can probably find a party, or you can do what I do and head for Patriot Place.
You can also take the train from South Station in Boston, which I tried once to see if it saved me any time (it didn't). I believe it leaves 2 hours before kick-off and at the end of the game a half hour after the game ends. Check the schedule. The train does save you the stress of driving, but then you have the stress of "am I going to make it on time?" By the time my train got there we had to run for our seats to make opening kick-off. I knew where I was going and you won't, so keep that in mind. You probably won't have any time for tailgating or eating beforehand. Others on here have taken the train and missed opening kick-off. Still, if you are not familiar with the area and nervous about driving, it might be a good option to try.
Bottom line - it can be stressful and expensive getting to a game. Once you make it there you will be bummed that you can't watch every game live. There is no substitute for it, IMO. If you can sit back and relax and ignore the dent in your wallet (something I always try to do if I am doing something special for myself), you will have a blast.