Newbie Runner - advice?

Holy moly! 3 miles on your first day?! Impressive that you could do it, but it's no wonder you feel sore, as AmyRhubarb said. It's called Delayed Onset Muscle Soreness (DOMS) and is normal when you start a new activity, especially if you do too much. And it is normal for arms, shoulders, trunk, etc. to feel it; you use those muscles running, too. Form might contribute: you should run with your torso upright, or just slightly leaning forward, and your arms should swing gently back and forth, with your forearms parallel to the road/track; don't pump back and forth vigorously. Try to keep your muscles relaxed, and keep your head up and looking ahead, not down at the ground (unless the surface is really uneven, in which case, slow down).

I'd suggest trying the Couch to 5K (C25K) program: http://www.coolrunning.com/engine/2/2_3/181.shtml

C25K builds up to running 5K (3.1 miles) by alternating running with walking, and gradually increasing the running bits while decreasing the walking. There's an app for it, but you don't need it, just a stopwatch to time the running vs. walking parts.

It's important to build up gradually in order to allow your muscles and joints to adapt to the stresses of running, especially your feet and knees. When you run, you put stresses on your knees equal to as much as 5 times your body weight. It takes a while for them to adapt.

Quality running shoes are important, too, though a bottom-end running shoe from a major manufacturer (Asics, Brooks, New Balance, Nike, Mizuna, Saucony, Salomon, etc.) will be fine for running under 20 miles a week. If you take your old shoes to a running store, the clerk should be able to look at how the soles are worn and suggest a shoe that works for your running style.

What everyone else has said is true -- 3 miles was too much for your first time every running. C25K is a great program and is based on alternating running/walking. Many 'beginner running' programs use this method. It will help to build up your muscles and avoid injury.

Someone else already mentioned that if you are going to stay under ~20 miles/week then you can buy a decent pair of store running shoes which you can often get on sale. However, if you really enjoy running and intend to run more than that or participate in races often then it's totally worth it to buy a good pair of running shoes, from a running store. Bring in your current running shoes and they look at the wear pattern usually and help you pick out a good pair based on your gait (there's a store near me that actually films you running too). And then once you have a really nice pair, only wear them running and keep track of your mileage on them so you know when they will need to be replaced.

Once you start running regularly, if you have bad shoes you'll know it pretty quickly. Best piece of advice is to LISTEN TO YOUR BODY. If something hurts....stop running. Like right now since you're really sore, I'd wait until you feel completely better to run again. Even if you feel something get tweaked during a run but feel like you can keep going....it's better to stop or slow down in order not to do serious damage. I pulled my piriformis muscle a couple years ago during a run (and continued running) and ended up not being able to run for 9 months. So listen to your body. Incorporate rest days as well as days you do a workout other than running too (cross training days).

Runners World is a great resource:
http://www.runnersworld.com/getting-started/the-8-week-beginners-program?page=single

Hi! Great job getting out and being active! I'm fairly new to running myself, only really being consistent in the last couple-few months. Good shoes are a MUST. I have a bad knee and hip, as well as plantar faciitis. I ran a few times on "inexpensive" (read: cheap) running shoes and my feet would always hurt, sometimes my toes would start to go to sleep half way through. I decided if this was something I was going to stick with, I needed to invest in some GOOD shoes. I went to a local running store that filmed my gait as I ran. I never would have known that I pronated when I ran, thus a shoe with more support was recommended. They were great to work with me to find something that wasn't too expensive and I was out the door for $80. My feet have thanked me ever since.

As for running itself, I would say listen to your body. It sounds to me like you may have run too far and too fast. My first several "runs" were just under 2 miles, and were more walking than running. I started out at about a 16 min/mile pace - sometimes longer, depending on the terrain. I'm still "wogging" as I call it; my pace is about a 13:30 mile, and I've bumped up my distance to just over 3 miles about 3 weeks ago. I have recently done a couple 4 or 5 mile outings on the weekends when I have more time, but always pay attention to how I'm feeling.

Also, as soon as your budget allows, get a heart rate monitor - it's the best piece of equipment to monitor your fitness progress.

Enjoy your running!