1. Take it slow. You may not be able to go out at the same pace you did at the end of last season. You'll get there, but it will take time and more workouts to get to that point. So, right now, just take it slow. Keep the pace easy. If you train with with RPE or HR make sure you're keeping within the appropriate range.
2. Stick with it. You haven't run this distance in awhile. Your body will have detrained and the physiological changes will make even shorter workouts feel long. You may feel great when during the first half of your run, but then start to wonder of your watch stopped half way through. First, make sure watch did not indeed stop working. Then, back off your pace by about 15-30 seconds per mile. Remember, this is your long, slow distance run. Even if it's not as far as you're used to running, it should still feel like a long run. If not, it's probably too short.
3. Hydrate. During this part of the season, your long run might seem short. But after your time off, your body needs to adapt again to the demands of a longer run. Your body might not require the insulin kick of Heed or Gatorade for these seemingly shorter distance long runs, but you will still benefit greatly from taking in enough water to stay hydrated.