More Structured Training

I've been running for around 16 months now.  Started off not being able to run for more than 30 seconds, joined a running club (who taught me to slow down!) and have since managed to complete 3 half marathons, with times of 2.30 hrs, 2.22 hrs and then 2.20 hrs.  I have also completed a 5k in 28 mins and a 10k in 61 mins.  I generally run 3 times a week - two 4/5 milers and one long run (longest run to date being 15 miles). 

I was wondering if anyone could give me some tips on how to take a more structured approach to my training?  I don't think I will ever be fast but would like to be able to get my half marathon time down to around 2.15 hrs if possible!  I was thinking of introducing intervals or hill training.  Also, should I increase the number of runs I do?  Should I be doing some none running exercise? 

Thanks in advance

Have a look at the training section of this site as there's a few plans that sound like they'd suit your needs.

I'd say you'll need to increase the number of runs and add a speed session to improve, but the plans should cover this.

I assume your running club will have a coach? Would probably be a good idea to ask their advice as they already know you and what you're already doing training-wise.

If you've only been running for less than 18 months and each half marathon has been faster than the last, I'd say you've probably got a lot more room for improvement in you than you think! 2:15 is a realistic time to aim for now but (without even knowing your age or whether you're male/female) I'd reckon with the right training you could do much better than that...

Like Styutyr says, think about adding a fourth run and doing some speedwork. Also if you're serious about getting faster, think about your weight. If you're at all overweight it will slow you down and losing extra weight is one of the easiest ways to improve your speed. Again, I don't know if you ARE overweight at all, I'm just mentioning it as most people could benefit from losing a few lbs.