This is the easiest way to incorporate more miles into your training:
-run a warmup run and a cool down run at 1-1.5 miles each and bam that's 2-3 more miles you'll have for the day
-warm up and cool down runs should be at a slow easy pace
-I used this while summer training in hs and college because some days just aren't good and you don't feel like going for an 8 mile run so I'd just do a 5 mile run with a 1.5 mile warm up and cool down and then I'd get my 8 miles for the day without pushing it.
-obviously if you keep taking miles from the actual run and using them in warm ups and cool down you'll loose training but it's also just an easy way to get an extra 3 miles in for the day to get more overall mileage if needed