Half Marathon Training Advice

I'm a 28 year old male and just got back into running a year ago after about a ten year break since HS track and XC. I've been really happy with my progress thus far, I did a 1:28 half at Hyannis in February and ran an 18:25 5k a few weeks ago which beat my HS 5k PR by a few seconds. I've got my eye on a half marathon in September and I'd love to get below 1:25. I'm wondering whether I should pick out a training plan or just stick to building a strong base. Over the past year i've probably averaged 30-35 mpw and I was thinking I'd just up that to 45-50 during the summer and try to get in a tempo run at race pace once a week. Thanks!