What's the best way for me to build up my running endurance again after a break?

There are some guidelines you can follow to avoid injuries and as an approach to training for competitions. Increase your weekly mileage no more than 10% a week. You don't say how much you are running now but, potentially, your plan starts with two 20 mile weeks (5 miles x 4 times). So if you you run 20 miles the first week you would add 10% and run 22 miles the second and 24.2 the third (you can round it off to 24). The 4th week should be a rest week and you should cut it back to what you started 4 week cycle with, 20 miles. The fifth week you continue, adding 10% to what you ran the third week, putting you at 26 miles.