For me it has a lot to do with where I am and who I am with, sometimes its the exact opposite of what worked before. The other day I ran alone and it was just great to watch the sun come up then the next day watching the sun come up I was thinking about a running club. Be careful on the distance, it does not take to much to get hurt. Still aim for one long run a week and speed work for less time. This will also give you less time away from home. Many long slow runs can be worse for you, intervals or tempo runs make you faster. Try not to do the same speed each run, challenge yourself to beat a previous time for the same run. Even in ultra runs speed work really can help, after a few weeks of speed work your slow run will be much faster than before even at that easy pace..