I'm pretty new to running and am hoping that someone can give me an answer to what's probably a really basic question. I started running regularly in September (I ran slowly once a week or so for a couple of years before that). I'm currently running 30-35 mpw, usually 2 10-mile runs and 2-3 5 mile runs, all at a comfortable pace. I ran my first 5K in March in about 21 minutes.
Should I keep building up the mileage, or should I start adding speedwork? I'm planning to run another 5K this fall and do my first marathon in January (I live in Texas). Thanks in advance for the comments.