Nothing better than a few good chocolate bars to sweeten up my day. With 18 miles a week, how long does each running session (each day) take you? I'm only starting to learn to approximate those things.
I like to alternate my mileage and pacing for variety. Every week I like to do a long slow run (6 to 8 miles), two 3 mile runs at a quick pace, a four or five miler with a lot of elevation, and a one miler at a very quick pace. So each run takes anywhere from 2 hours to 30 minutes, with stretching and cool down walking. Of course a lot of this just depends on what you prefer. I like to run in the afternoon after work, while many people enjoy running in the morning or only have time in the morning. Some people prefer to run by time, not distance. And some prefer to run the same distance everyday. Find what works for you! EDIT: I use a website called RunMyRoute to map out my routes and mileage. Or if you prefer to run by time, I'd say just approximate how long it takes you to run a mile and just multiply that by how many miles you want run. Take an extra 15-20 minutes for warm up/stretching/cool down.
No problem! Warming up is going for a quick, very slow jog before stretching. This is important, as stretching cold muscles is less effective than muscles that have been warmed up by jogging a block or two. Then you can do a few stretches. I just stretch the basics: quads, hamstrings, calves. I also stretch my hip flexors, since I've had trouble with them in the past. I like to start my run slow and build up to whatever pace I am aiming for that day. Injuries occour when you overuse an area or you transition to quickly from a resting state to a more high intensity pace. Cool down is also important. I like to walk another block or two after finishing a run to allow my muscles to transition more smoothly to a resting state. Stretching is also important after running, as it releases lactic acid that built up during your run, as well as allowing blood to flow more effectively into those areas that you exercised and need nutrients the most. Stretching after you run is actually more important tha stretching before you run, believe it or not.