Bike improvements: speedwork or long slow rides.

Conbination of both.

 I would change the long easy miles to long steady miles on some days and intervals on others.

You need to incorporate intervals 1-2 times per week to stress your body.  The long easy rides should be done at an aerobic pace. 

As to your running, you need to do the same there. Speedwork along something like this.

Week 1 30sec fast/30sec easy X6

Week 2 30sec fast/30sec easy x10

Week 3 x12

Week 4 bump up to 1 min intervals going down to 5 of those. 

These are just examples only to help improve.  Recovery should be a jogging pace and not walking.

In my experience, in order to get fast on the bike one needs to push it hard in training.  Not all of the time, but a significant amount of time (unlike with running), while also logging enough miles to be able to maintain it.  I've tried both approaches.  When I logged a lot of miles on the bike and didn't push the pace, my endurance was good and I felt good getting off the bike to run in races, but I couldn't suddenly find that extra gear on the bike in a race if I hadn't done it in training. 

In my experience with running, putting in more easy miles makes me much faster in races even without speedwork.  I guess the same methodology doesn't apply to cycling.  

I usually do about 2 of the 4 bike rides per week at a pretty high effort.  85-90% of my MHR.  The other 2 are usually to spend some time in zone 1 and build my aerobic system.  I have made some pretty big improvement since I've started riding regularly but just wanted to see if I was going about training the right way at this point in my cycling career.

The same methodology does work for running in theory.  The problem is the recovery cost and injury risks of too much high intensity running.

Following up on Jason's comment. 

Yes, there's a difference between run and bike training guidelines. You're doing well if you've figured that out so soon.

From the perspective of building the aerobic systems, there needn't be any difference between run and bike training, as you're trying to achieve basically the same effect. And a balance of medium and high intensity workouts should be good for that.

But there are a few reasons for the difference in guidelines, as far as I can tell.

(i) As Jason mentioned, recovery from the impact of running, and the risk of injury from high intensity / high impact training shifts the balance away from an interval training focus in running.

(ii) But there's also a positive reason why the steady running is recommended more than steady biking. The mere act of training our bodies to withstand the pounding and the repetitive eccentric muscle contractions of running has a benefit. It's often described as benefiting run 'efficiency', but it's less well understood than the aerobic training mechanisms (... at least, around here; I've not yet seen a good account of what this involves)

(iii) For many people, the effort level of a 'steady' run is comparable to the effort level of a moderately intense bike ride. You can ride at a very low intensity and you're still riding, but if the run effort gets lower you start jogging or even walking. So to some extent we're comparing apples and oranges here.

Good news for you is that since you're young and fairly light, you can likely recover from higher intensity running better than many of us around here. You would still do well to establish a solid base of steady miles, but the risks of higher intensity running are lower. It sounds like you're making good progress already. And welcome to BT - do keep being part of the conversation.