Over and over again people recommended autumn for thinner crowds, cooler temps, and a more peaceful experience. The tress in Pennsylvanian are stunning in the fall.
When not to go - July. From everyone I have spoken to this is the most heavily visited month of the year.
However, the Battle of Gettysburg took place July 1, 2 & 3, 1863. If being there on those dates of remembrance is important to you, there is an annual reenactment of the battle. Here is information to purchase tickets to that event. http://www.gettysburgreenactment...
More men died in the Battle of Gettysburg than any other battle fought on American soil before or since. The 3,965 acres of the Gettysburg Battlefield is managed by the National Park Foundation. You can easily spend a full weekend at this massive historic site or just a few hours, easily tailoring a visit to your needs and interests. President Lincoln said in his Gettysburg Address regarding the preservation of the land, “We have come to dedicate a portion of that field as a final resting place for those who here gave their lives that that nation might live. It is altogether fitting and proper that we should do this."
First stop - main visitor center for bathrooms and a map. There are no fees to enter the Battlefield or to park. Go early in the day if you are able to get a lay of the land and park without trouble. There are tickets you can purchase for ranger tours or historic home visits, but all of these are optional. You can download free podcast audio tours here http://www.civilwartraveler.com/... and be on your way skipping tickets lines and dodging crowds.
If history isn't quite your thing, there are abundant and beautiful trails. Here's a link to consider routes http://www.alltrails.com/us/penn...
The historic town of Gettysburg, PA surrounds the Battlefield. You will have to show will power and decline many Ghost Tours that are promoted by shop keepers. Of course if you love ghost tours, just do a little Googling prior to find out the most highly recommended tours.
If you want to grab a bite to eat & drink the best place we found was Battlefield Brew http://battlefieldbrewworks.com/ which is located in an old grain storage building that was used as a Confederate field hospital during the Civil War. You can get a local brew and justify it was for history sake.
*There are more than 1,400 monuments, markers and tablets at Gettysburg.
*More than 30,000 dead and wounded soldiers were left in the battle's wake.
*The Battle of Gettysburg started without the knowledge or consent of either army commander -- Lee or Meade.
*The 200,000,000 year-old Gettysburg Sill created the volcanic boulders on the Union right and left flanks.