Whenever I go to a new city I much prefer visiting it on foot - it's good exercise and it gives me way more time to take in all the different sites. In Concord, however, I quickly realized that I would have to spend most of the day driving around in my car. Even though downtown Concord is fairly compact, the different museums and attractions are all located at least a mile outside of the town center, all in different directions. This makes it practically impossible to visit the town on foot, especially when you have to deal with fixed guided tour hours. The good news is that free parking is available at all the different sites, but if you really don't feel like driving, I'd recommend bringing your bicycle as the quiet country roads make for some really nice rides!
From the Route 128/95 belt around Boston, take Route 2A west straight into Concord centre. Or, take the MBTA commuter rail from North Station in Boston to the Concord rail stop. If you're really adventurous, start on bike at Porter Square in Cambridge and use the Minuteman Bikeway and the Battle Road Trail to Concord, passing through historic Lexington as well.
While driving is the most easy and obvious way to get around this mainly rural/suburban area, it can be pleasant to stroll or bike the winding, narrow country roads as well.