Coming back from a running injury stinks. But, it stinks a lot less than the time spent actually dealing with the injury. The first and perhaps most important thing to keep in mind when getting back to running after a long hiatus due to injury or an accident: Be grateful for every mile.
Injures have a way of giving runners a bit of a reality check; in coming back from all that time spent rehabbing and cross-training, it is important to retain that perspective and not get greedy with miles. The last thing you want during a comeback is to re-injure yourself, or to get a new injury, so keep the following in mind as you return to running.
The Slow Build
The second you get the green light to begin running does not mean you can jump full-force back into where you left off. It is important NOT to rush things, as patience pays off in the long haul. Gradually increase the amount of time you spend running and supplement the rest with cross-training.
Don't Slack on PT
Many runners, upon getting over their injury, start to get lax on their physical therapy or other rehab exercises. Don't get comfortable and forget that, in order to prevent getting injured again, you still need to keep up on your preventative care.
After a long break, you need to chuck out any and all comparisons to your runner self pre-injury. It will only set you up for frustration and can ultimately derail your comeback. Track the progress you make post-injury and take every victory (ie: extra miles, faster workouts, etc.) as it comes. Eventually you'll return to "old you" workouts and times, but before you hit that realm think of yourself with a totally clean slate.
Miracle of Muscle Memory
Oh how those first few runs will whip your butt! The important thing is to remember that while those first runs will feel like you've got legs that have never run a step in their lives, the good news is, thanks to muscle memory, if you've been a runner for a number of years, you'll snap back into fitness rather quickly. The first couple of weeks will be rough, but stick it out and you'll be motivated by the progress that follows.