The best advice I've read

This guy's question was whether increasing his long by one mile per week is safe in preparing for a half marathon. He's currently at a 10k long.

For the athletes I coach, I like to prescribe training in four-week cycles. As a general rule of safe practice, I’ll increase the length of one’s longest run of the week by no more than 15 percent for three consecutive weeks before pulling it back a few miles in the fourth week. The body needs a chance to adapt to the increased level of stress being placed upon it, so reducing your long run and cutting back on your overall mileage every fourth week or so in a given training cycle is an effective way to do just that and will also lessen the likelihood of injury.

In your case, I’d cover 7.2., 8.2, and 9.2 miles for your long run each of the next three weeks, then cut it back to 6.2 miles the fourth week. At the start of the next cycle, pick back up where you left off, starting at 9.2 miles, then upping it to 10.2 and 11.2 before dialing it back to 8.2 miles in Week 8. On the third four-week go-around, start at 11.2 miles, then 12.2 and before you know it, in less than 12 weeks you’ve safely worked your way up to covering the half marathon distance.